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Stability of Citrate, PVP, and PEG Coated Silver Nanoparticles in Ecotoxicology Media
Abstract
Silver nanoparticles (AgNPs) are present in the environment and a number of ecotoxicology studies have shown that AgNPs might be highly toxic. Nevertheless, there are little data on their stability in toxicology media. This is an important issue as such dynamic changes affect exposure dose and the nature of the toxicant studied and have a direct impact on all (eco)toxicology data. In this study, monodisperse citrate, PVP, and PEG coated AgNPs with a core size of approximately 10 nm were synthesized and characterized; their behavior was examined in standard OECD media used for Daphnia sp. acute and chronic tests (in the absence of Daphnia). Surface plasmon resonance, size, aggregation, and shape were monitored over 21 days, comparable to a chronic exposure period. Charge stabilized particles (citrate) were more unstable than sterically stabilized particles. Replacement of chloride in the media (due to concerns over chloride-silver interactions) with either nitrate or sulfate resulted in increased shape and dissolution changes. PVP-stabilized NPs in a 10-fold diluted OECD media (chloride present) were found to be the most stable, with only small losses in total concentration over 21 days, and no shape, aggregation, or dissolution changes observed and are recommended for exposure studies.
... Antibiotic resistance comes from changes in the structure of bacteria due to changes in the genetic material or through the acquisition of genetic material from external sources, [57,58] Ag NPs and Au NPs are loaded into polymer-based hydrogels with a porous structure, such as alginate [59], chitosan [27,60], gelatin [61], konjac glucomannan [23], hydroxypropyl methylcellulose [24], carboxymethyl cellulose [13], carboxymethyl chitosan [62], polyvinyl alcohol [37], carbopol [63,64], gelatin methacrylate [65], polyacrylamide [40], polyethyleneimine [66], and polyvinylpyrrolidone [40,63,[67][68][69]. Occasionally, hydrogels exhibit poor mechanical properties, and other agents are required as additives in the manufacturing process, such as tannin acid [60], graphene [66,[70][71][72], aluminosilicate nanotubes (NTs) [65], and metal-organic frameworks (MOFs) [69]. ...
... The polymer-based hydrogels help to control the morphology and size of the nanostructures and participate as a stabilizing medium for nucleation sites to produce silver seeds [13,66]. Biocompatible polymers, such as chitosan [27], konjac glucomannan [23], carboxymethyl cellulose [13], carboxymethyl chitosan [62], polyvinyl alcohol [37], carbopol-934 [63], graphene [41,[70][71][72], gelatin methacrylate [65], polyacrylamide [40], polyethyleneimine [66], and polyvinylpyrrolidone [40,63,[67][68][69], have been used to fabricate antibacterial and antibiofilm materials. ...
... Ryan et al. [136] synthesized a chitosan and siloxane hydrogel to incorporate Au NPs. Tetraethyl orthosilicate (TEOS) was used to form an interpenetrating polymer network and improved the hydrogel structural properties, such as flexibility and strength (67)(68)(69)(70)(71)(72)(73)(74). The size distribution of the Au NPs was 19 nm ± 18%. ...
The development of multidrug-resistant (MDR) microorganisms has increased dramatically in the last decade as a natural consequence of the misuse and overuse of antimicrobials. The World Health Organization (WHO) recognizes that this is one of the top ten global public health threats facing humanity today, demanding urgent multisectoral action. The UK government foresees that bacterial antimicrobial resistance (AMR) could kill 10 million people per year by 2050 worldwide. In this sense, metallic nanoparticles (NPs) have emerged as promising alternatives due to their outstanding antibacterial and antibiofilm properties. The efficient delivery of the NPs is also a matter of concern, and recent studies have demonstrated that hydrogels present an excellent ability to perform this task. The porous hydrogel structure with a high-water retention capability is a convenient host for the incorporation of the metallic nanoparticles, providing an efficient path to deliver the NPs properly reducing bacterial infections caused by MDR pathogenic microorganisms. This article reviews the most recent investigations on the characteristics, applications, advantages, and limitations of hydrogels combined with metallic NPs for treating MDR bacteria. The mechanisms of action and the antibiofilm activity of the NPs incorporated into hydrogels are also described. Finally, this contribution intends to fill some gaps in nanomedicine and serve as a guide for the development of advanced medical products.
... Silver nanoparticles disturb this balance, exerting a toxic effect on these microorganisms [142]. Coating also influences the transformation of AgNPs in the environment; for example, greater stability and less size changes were observed for AgNPs coated with polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) compared to AgNPs coated with citrate [143]. The determination of the possible ways of transformation of silver nanoparticles and the parameters that affect it is crucial in the assessment of the complex toxicity of AgNPs. ...
... The main purpose of this technique is to minimise environmental toxicity and health threats [144,145]. To overcome this problem, scientists discovered exact pathways using naturally occurring sources and their products that can be used to synthesise nanoparticles [143,146]. Biological methods are extremely valuable as they utilise natural processes to synthesise nanoparticles. In the 19th century, scientists discovered the reduction ability of biological materials, laying the foundations for future green synthesis [147]. ...
In recent years, research on silver nanoparticles (AgNPs) has attracted considerable interest among scientists because of, among other things, their alternative application to well-known medical agents with antibacterial properties. The size of the silver nanoparticles ranges from 1 to 100 nm. In this paper, we review the progress of research on AgNPs with respect to the synthesis, applications, and toxicological safety of AgNPs, and the issue of in vivo and in vitro research on silver nanoparticles. AgNPs’ synthesis methods include physical, chemical, and biological routes, as well as “green synthesis”. The content of this article covers issues related to the disadvantages of physical and chemical methods, which are expensive and can also have toxicity. This review pays special attention to AgNP biosafety concerns, such as potential toxicity to cells, tissues, and organs.
... The stability, shape, and size of the prepared particles depend on the reaction conditions (temperature, time, mixing, light/darkness, pH) and the reagents used (chemical structure, molecular weight of polymers, dose, ionic strength, etc.) [35][36][37][38][39]. Control of Metals 2024, 14, 513 7 of 15 nucleation kinetics during synthesis by mutual ratio, combination, and order of addition of stabilizing/capping agents can influence the shape, size, and aggregation of particles [40,41]. ...
The research aimed to observe the influence of the storage conditions of silver colloidal solutions prepared by biological (green) and chemical methods on their long-term stability. Green methods for reducing and stabilizing silver nanoparticles (AgNPs) use natural substances. The rosemary leaf extract was used for AgNPs synthesis, and prepared nanoparticles were spherical (average size of 12 nm). In the chemical method, commercial chemicals (NaBH4, TSC, PVP, and H2O2) were used, and two colloids were prepared; the first contained spherical nanoparticles with an average size of 8 nm, and the second triangular prisms with an average size of 35 nm. The prepared colloids were stored under four conditions: at room temperature in the light and the dark, and at a temperature of 5 °C (refrigerator) in the light and the dark. The results confirmed the influence of storage conditions on the stability of nanoparticles. Colloids stored at 5 °C in the dark show the best stability. However, differences in stability dependent on the shape of nanoparticles prepared by chemical method were also observed; triangular nanoparticles showed the least stability. Methods such as UV–vis spectrophotometry, TEM, and EDX were used to analyze the nanoparticles before and after storage.
... The coauthors of this manuscript consist of members of an ECETOC Expert Group (Table S2 †) but others may be relevant; properties of particle itself considered and not surrounding media. 25,97,100,122,[126][127][128][129][130] Environmental Science: Nano Perspective (comprising members from industry, CROs and academia). The views expressed in this article are solely those of the coauthors and may not represent those of the sponsoring organisations. ...
Following available approaches included e.g. , in existing OECD Test Guidelines and Guidance Documents for the aquatic testing of particulate materials such as nanomaterials and microplastics leads to various challenges to be considered.
... Further research is needed to determine the precise process underlying the nanoparticle creation 7,11 . AgNPs are not very stable in humid environments 25,26 . The key to successful silver nanoparticle preparation is preventing the development of aggregates. ...
Highly effective AgNPs@C was efficiently synthesized by electrical arc powered by single spark unit which was sufficient to ionize the dielectric media (deionized water) through applying strong electric field between the electrodes (silver and carbon). The AgNPs@C shell was characterized in terms of stability, morphology and phase structure. All characterizations showed that the prepared silver nanoparticles were spherical with average size reached 17 nm coated with carbon shell. The antibacterial effect of the synthesized nanoparticles was tested against Pseudomonas aeruginosa in comparison to Ceftazidime (commonly used antibiotic against P. aeruginosa infections). It was revealed that AgNPs@C shell has superior activity with inhibition zone diameter reached 15 mm and minimum inhibitory concentration reached 2 µg/mL. The observed activity was further confirmed by confocal microscope which showed an increased red region, representing the dead cells, correlated with the presence of AgNPs@C. Moreover, transmission electron microscope studies implied the possible AgNPs@C antibacterial mechanism of action was the nanoparticles adherence to the bacterial membrane causing cell lysis. The molecular studies against fimH (virulence adhesion gene), rmpA (mucoid factor encoding gene), and mrkA (biofilm forming gene) proved the inhibition of their genetic expression. The cytotoxic effect of the synthesized AgNPs@C showed CC50 reached 235.5 μg/mL against normal lung cells (L929 cell line).
... These coatings are very often used to provide these different hydrophilicities. The Ag-CIT NPs were considered the uncoated Ag NPs, since due to its weak bound to the core Ag [11], this coating is easily lost once the NPs are suspended in an aqueous medium. Therefore, the obtained manufactured NPs were TiO 2 uncoated (TiO 2 -UNC), TiO 2 -CIT, TiO 2 -PEG, TiO 2 -DDPA, CeO 2 -UNC, CeO 2 -CIT, CeO 2 -PEG, CeO 2 -DDPA, Ag-CIT, Ag-PEG and Ag-OAM. ...
The peculiar physico-chemical characteristics of nanomaterials (NMs) and the use of different coatings to improve their expected properties result in a huge amount of nanoforms, which vary in chemical composition, size, shape and surface characteristics. This makes it almost impossible to test all the nanoforms available, and efforts have been made to establish grouping or read-across strategies. The aim of this work was to find a behavior pattern of effect among nanoforms of different metallic core nanoparticles (NPs) (TiO2, CeO2 and Ag NP) with the same coatings (sodium citrate, poly (ethylene glycol), dodecylphosphonic acid or oleylamine). Daphnia magna, rainbow trout and two fish cell lines (PLHC-1 and RTH-149) were exposed to a range of concentrations (up to 100 mg/L) of the uncoated or coated NPs. Ag NPs were the most toxic, followed by CeO2 NPs and finally by TiO2 NPs. The results show that a clear pattern of toxicity in the studied species could not be established related to the coatings. However, it was possible to confirm different inter-species sensitivities. RTH-149 was the most sensitive cell line, and Daphnia magna was more sensitive than fish. Moreover, some differences in coating-core interactions were found between the metal oxide and the metal NPs in Daphnia magna.
... The size of the particles also affected the dissolution of these NPs in the media. This was also observed with TiO 2 NPs and AgNPs which demonstrated different dissolution and accumulation characteristics in animal cell culture media based on their size (Ji et al., 2010;Tejamaya et al., 2012). ...
Abstract
Hairy root culture is one of the promising biotechnological tools to obtain the stable and sustainable production of specialized metabolites from plants under controlled environment conditions. Various strategies have been adopted to enhance the accumulation of bioactive compounds in hairy roots yet their utilization at the commercial scale is restricted to only a few products. Recently, nanotechnology has been emerged as an active technique that has revolutionized the many sectors in an advantageous way. Elicitation using nanoparticles has been recognized as an effective strategy for enhancing the bioactive compounds of interest in plants. Nanoparticles elicit the activity of defense-related compounds through activation of the specific transcription factors involved in specialized metabolites production. This review discusses the recent progress in using nanoparticles to enhance specialized metabolite biosynthesis using hairy root culture system and the significant achievements in this area of research. Biotic and abiotic elicitors to improve the production of bioactive compounds in hairy roots, different types of nanoparticles as eliciting agents, their properties as dependent on shape, most widely used nanoparticles in plant hairy root systems are described in detail. Further challenges involved in application of nanoparticles, their toxicity in plant cells and risks associated to human health are also envisaged. No doubt, nanoparticle elicitation is a remarkable approach to obtain phytochemicals from hairy roots to be utilized in various sectors including food, medicines, cosmetics or agriculture but it is quite essential to understand the inter-relationships between the nanoparticles and the plant systems in terms of specifics such as type, dosage and time of exposure as well as other important parameters.
... The dye was not determined in the first 30 min but its reduction was possible using pristine nano-silica although it couldn't resist bacterial growth. The presence of O 2 , Cl − , PO 4 − , and organic molecules also has a strong impact on the antibacterial performance of AgNPs [127,128]. The interaction of these agents causes a change in the composition and structure of AgNPs. ...
With increasing the biological contamination in drinking water day by day, the demand for fresh drinking water is also increasing. The limitations of current traditional water disinfection approaches demand the development of novel, safe, low-cost, and highly efficient techniques as alternatives. With the evolution of nanotechnology, the magnificent antimicrobial properties of silver nanoparticles (AgNPs) have started to be used broadly in water disinfection. Recent studies reflect that AgNP-based water disinfection methods are highly promising to replace conventional water disinfection methods simply and cost-effectively. To improve the efficiency of water disinfection with AgNP-based matrices, a clear understanding of the factors, affecting the water disinfection process is very much required. This review article comprises a complete discussion about the AgNPs incorporated matrices, effective for water disinfection starting from their synthesis to probable mechanism of action including the factors which control the water disinfection efficiency of those materials. This review article will be helpful to the competent authorities and researchers, working to improve water disinfection techniques, to develop more effective strategies with AgNP-based water disinfectant.
... The observation shows that the chemical constituents of the extract could protect the synthesized AgNPs from aggregation. It was supported by no increasing peak intensity at a longer wavelength (Tejamaya et al., 2012). The negative charge of the particles owing to the chemical constituent of extract capping the particles produces negative-negative repulsion that protects the particles aggregation. ...
Silver nanoparticles (AgNPs) have been synthesized using Rhoeo discolor leaf extract as a reducing and stabilizing agent. AgNPs were synthesized by adding silver nitrate to the extract of Rhoeo discolor and incubating it in a boiling water bath. The change in color of the mixture from clear to yellow indicated AgNPs formation. The synthesized AgNPs were spherical and showed an absorption peak at around 410-420 nm. The size of particles was distributed from 92 to 485 nm with an average size of 176 nm, and the polydispersity index was 0.185. The stability test showed that synthesized AgNPs were stable for three months of storage at ambient temperature. The extract of Rhoeo discolor were responsible for reducing silver ion and stabilizing the synthesized AgNPs.
... It can reduce the dosage of more expensive NMs, reduce the input of agricultural production costs, and alleviate environmental pressure, which is also more practical for the future large-scale promotion of nano-agriculture. Organic macromolecules such as humic acid and fulvic acid, when mixed with NMs, can enhance the stability of NMs and reduce material settling (Tejamaya et al., 2012) (Fig. 5a). In addition, humic acid contains oxygen functional groups (-COOH and phenol-OH) that can corrode insoluble phosphorus (Du et al., 2020) and also increase the mobility and migration of P when it is applied with nano-phosphate fertilizers, thus increasing the effective phosphorus content in the inter-fertilizer microdomains (Du et al., 2012). ...
... The physisorbed coatings have already been studied in terms of environmental fate and toxicology. Citrate, gum arabic, copolymers, and other additives are commonly adsorbed onto nanomaterials to improve dispersion in a desired solvent [52]. Surface modification approaches for nanomaterials, on the other hand, are carried out with rather complex heterocyclic structures that are covalently bound to the nanomaterial surfaces [53]. ...
The combination of multiple nanomaterials has recently become the focus of materials development. This novel material class is known as nanohybrids. Recently, there has been a focus on the conjugation of two or more nanomaterials in order to achieve increased multifunctionality while also enabling for next generation materials with improved performance. The importance of studying novel nanohybrids with their multidimensional and complex behaviour is enormous, and there is a growing interest in their applications. With the increased production and potential use of nanohybrids comes concern about their properties and characteristics, which are responsible for their improved performance in a broader range of applications. Hence, this chapter session provides a comprehensive report on the various types of nanohybrids and their synthesis methods. Their broader applicability was discussed, with a focus on their use in water treatment. Furthermore, this chapter discusses the prospects of nanohybrids in material science.
... Recent statistics show that AgNP is the most investigated and commercialised NP compared to other noble metals, which account for 55.4% of the total nanomaterial-based consumer goods available in the market as it is inexpensive, has good conductivity, chemical stability, catalytic activity, antibacterial activity, etc. Xu, 2006;Tejamaya, 2012;Sharma et al., 2009;Marciniak, 2020;Huang, 2018;Dobias and Bernier-Latmani, 2013;Agnihotri et al., 2014). Due to their special features, AgNP is used in a wide range of fields. ...
In this work is investigated the effect of nonthermal plasma reactor configurations on the synthesis of silver nanoparticle (AgNP) comparing three reactor configurations: (i) coaxial dielectric barrier discharge (DBD), (ii) like-free ground DBD, and (iii) corona plasma discharge. To make the AgNP synthesis cost-effective and eco-friendly, no reducing agent was used and to get stable particles , instead inexpensive sucrose was used as capping agent. The formation and stability of AgNP were verified using ultraviolet-visible (UV-Vis) spectroscopy and energy dispersive spectroscopy (EDS). The concentration and stability of AgNP were found to be dependent on various process parameters, with the optimal conditions of applied voltage, gas flow rate, treatment time, nozzle distance, silver nitrate concentration and sucrose concentration determined at 12 kV, 1.5 L/min, 180 s, 1.0 cm, 0.5 mM, and 20 mM, respectively. The surface morphology and particle size distribution (PSD) obtained with transmission electron microscopy (TEM) showed that the nanoparticle (NP) synthesized by coaxial DBD and corona plasma were spherical in shape with a wide PSD, and their average size was 6.2 nm and 9.6 nm, respectively. On the other hand, those NP synthesized by like-free ground DBD were mostly spherical, along with a few hexagon and triangular shapes. With like-free ground DBD, the PSD was found to be significantly narrower, and the average particle size was 20 nm which is bigger compared to NP synthesized by coaxial DBD and corona plasma. Better performance of AgNP synthesis by the like-free ground DBD is most likely due to higher energy delivery capacity.
... Regarding the promising effects of synergism between NPs and surfactants, utilizing stable surfactants was assumed at high salinity and high temperature conditions to stabilize the NPs in a suspension as a highly-recommended approach [20]. Efficient surfactants and polymers being utilized in the literatures can be summarized as sodium dodecyl sulfate (SDS) [10,[21][22][23][24][25][26][27][28][29][30], sodium dodecyl benzene sulfonate (SDBS) [31][32][33][34][35][36][37][38][39], cetyl trimethyl ammonium bromide (CTAB) [40][41][42][43][44][45][46], dodecyl trimethyl ammonium bromide (DTAB) and sodium octanoate (SOCT) [40,47], hexadecyl trimethyl ammonium bromide (HCTAB), polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) [48][49][50][51][52], Arabian gum [53,54] and guar gum [55,56]. The appropriate selection of surfactants is regarded as the most significant part of the surfactant-assisted chemical EOR procedure. ...
One of the most important aspects to use the nanofluid flow through the oil recovery process is physical and chemical constraints at high salinity and temperature, harsh conditions, leading to the instability and further problems. In this study, the stability of various nanoparticles, Al 2 O 3 , SiO 2 , ZrO 2 , TiO 2 , Fe 2 O 3 , nanoclay, and ZnO, were examined upon the concentration (0.01 to 3 wt%), temperature (ambient and 75℃), salinity (20,000 to 80,000 ppm), pH (2 to 12), and stabilizers of polyethylene glycol, polyvinylpyrrolidone, guar gum, Triton X-100, sodium dodecyl sulfate, cetrimonium bromide. Then, the most stable nanofluid was nominated to investigate the oil recovery mechanisms by performing interfacial tension (IFT), wettability alteration, and micromodel flooding analyses. Zinc oxide and silicon dioxide nanofluids were maintained their stability at the harsh conditions and guar gum showed a good performance in stabilizing nanofluids, compared to other nanofluids agglomerated. According to the results of the IFT reduction upon the nanofluid and reservoir crude oil (1.64 mN/m), wettability alteration of carbonate cores (113.68 degree) and micromodel experiments (additional recovery of 32.23% and 6.27% in the secondary and tertiary flooding, respectively) all compared to the seawater, the ZnO nanofluid stabilized by guar gum was an excellent candidate to use in the oil recovery projects.
... In the case of GSH-SAgNPs, an SPR peak at 385 nm reflects a size of 11 nm, as mentioned previously. 42 Our HAgNPs' SPR value agrees with previous findings (460−600 nm) 43 and is governed by the size and shell thickness. The red shift in the SPR value is because of the core− shell microstructure of the nanoparticles. ...
... Additionally, citrate was present on the AuNP surface as a stabilizing agent therefore can be easily displaced thereby encouraging nanoparticle agglomeration. These authors also concluded that the rate of dissolution depends on the type of functional group attached to the nanoparticle surface [59][60][61]. ...
The potential for nanoparticles to cause harm to human health and the environment is correlated with their biodurability in the human body and persistence in the environment. Dissolution testing serves to predict biodurability and nanoparticle environmental persistence. In this study, dissolution testing using the continuous flow through system was used to investigate the biodurability and persistence of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2 NPs) in five different simulated biological fluids and two synthetic environmental media to predict their behaviour in real life situations. This study examined the physicochemical properties and agglomeration state of gold, silver and titanium dioxide nanoparticles before and after dissolution tests using three different techniques (UV-vis, XRD and TEM). The UV-vis spectra revealed that all three nanoparticles shifted to higher wavelengths after being exposed to simulated fluids. The titanium powder was found to be mixed with both rutile and anatase, according to XRD examination. The average diameter of gold nanoparticles was 14 nm, silver nanoparticles were 10 nm and titanium dioxide nanoparticles were 25 nm, according to TEM images. The gold and silver nanoparticles were observed to be spherical, but the titanium dioxide nanoparticles were irregular in shape, with some being spherical. The level of dissolved nanoparticles in simulated acidic media was higher in magnitude compared to that dissolved in simulated alkaline media. The results obtained via the continuous flow through dissolution system also displayed very significant dissolution rates. For TiO2 NPs the calculated half-times were in the range of 13–14 days, followed by AuNPs ranging between 4–12 days, significantly longer if compared to the half-times of AgNPs ranging between 2–7 days. AuNPs and TiO2 NPs were characterized by low dissolution rates therefore are expected to be (bio)durable in physiological surroundings and persistent in the environment thus, they might impose long-term effects on humans and the environment. In contrast, AgNPs have high dissolution rates and not (bio)durable and hence may cause short-term effects. The results suggest a hierarchy of biodurability and persistence of TiO2 NPs > AuNPs > AgNPs. It is recommended that nanoparticle product developers should follow the test guidelines stipulated by the OECD to ensure product safety for use before it is taken to the market.
... The PVP, PEG, and dextran-capped AgNPs were synthesized using the same method as for uncapped AgNPs; however, before the reduction process was carried out, AgNO 3 was homogenized with PVP/PEG/dextran solution [54][55][56][57][58][59][60][61][62][63]. These polymer act through the interaction of the lone pair of electrons on the nitrogen and oxygen atoms with the silver ions thus creating a polymer layer around the ions preventing their aggregation via steric hindrance [64] (Fig. 1B, C). ...
Sofosbuvir has demonstrated several advantages over the traditional anti-hepatitis C (HCV) therapies; however, it has been found susceptible to hydrolysis and has a risk of hepatic carcinoma. The development of drug nanoparticles allows reduced side effects and increased stability. Silver nanoparticles have long been explored for their intrinsic antiviral characteristics. Therefore, the silver nanoparticles of sofosbuvir were synthesized and capped with various polymers including polyvinylpyrrolidone, polyethylene glycol, and dextran. The stable charachterized surface plasmon resonance band of AgNPs was achieved via optimizing various parameterters for instance volume and concentraion of reducing agent, ratio of ligand and metal, rate of mixing, and pH of medium. The AgNPs and drug-loaded nanoparticles were characterized by UV spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS), and zeta potential techniques. The 20–70 nm sized, round, negativly charged dextran-capped and dextran-reduced, nanoparticle were found to be the most stable and monodispersed in aqeous medium for 6 weeks at room temperature and 4 °C. Furthermore, both formulations were evaluated for drug release 90% of the drug was released from the formulations after 23 h while 99% was found to be released after 6 days. Dextran capped sofosbuvir–AgNP was found non-toxic to Huh-7 cell line as compared to the drug. Combined these results indicate that when sofosbuvir is encapsulated in the NP formulations, the formulations show intact potent anti-HCV activity in a less cytotoxic way.
... AgNPs released from commercial textiles during washing and from outdoor facades after rainfall events [85,86] would likely transform into agglomerates once dissolved in the aqueous solution [87][88][89][90][91]. Other than that, the combination of oxidation and reduction for Ag under light encourages the increased agglomeration of AgNPs as well. ...
Citation: Mat Lazim, Z.; Salmiati, S.; Marpongahtun, M.; Arman, N.Z.; Mohd Haniffah, M.R.; Azman, S.; Yong, E.L.; Salim, M.R. Distribution of Silver (Ag) and Silver Nanoparticles (AgNPs) in Aquatic Environment. Water 2023, 15, 1349. Abstract: Nanomaterials, classified as emerging pollutants that are toxic to the environment, are known to bioaccumulate across different trophic levels in the aquatic ecosystem. This study therefore investigates the distribution of silver and silver nanoparticles (AgNPs) in the aquatic environment of Skudai River, Johor, Malaysia. Water, sediment, plant, and fish samples were collected seasonally along four sites along Skudai River between May 2018 and April 2019. All samples were subjected to Ag analysis using an inductively coupled plasma mass spectrometer (ICP-MS). The analysis demonstrated that the concentration of Ag detected in water samples ranging from 0.001 to 0.505 mg/L was the lowest, whereas in the plants, 0.235 to 4.713 mg/kg of Ag was quantified. The upper sediments contained 0.036 to 28.115 mg/kg of Ag, whilst fish samples presented the highest accumulation of Ag, averaging between 9.144 and 53.784 mg/kg of Ag. Subsequently, the formation of silver nanoparticles was further proven by TEM-EDX analysis, where the detected size of AgNPs ranged from 20 nm to 35 nm. The overriding conclusion implied by bioaccumulation factor (BAF) and biota-sediment accumulation factor (BSAF) calculations suggested that Skudai River was indeed polluted by Ag and AgNPs. The values obtained stipulated that silver accumulation is occurring at an alarming rate and could therefore endanger fish consumers.
... The AgNPs synthesized using leaf extract was found to be stable in the aquatic environment (Sun et al., 2014). Stability of nanoparticles can be regulated by controlling the particle size and surface capping or through functionalization techniques (Sharma et al., 2014;Tejamaya et al., 2012). Furthermore, optimizing the processing conditions have an effect in producing stable nanoparticles. ...
... Optimisation of the chemical synthesis process is a very labour-intensive, costly and time-consuming task because it includes multiple reagents and different independent experimental conditions including the types and concentrations of reactants, temperature, reactor design and mixing conditions. For example, the size of AgNPs strongly depends on both the type and concentration of stabilizing agent [2], [3], [4] and often depends on pH of the solution [5], [6], [7]. Ionic stabilizers such as citrate used in this study produce a charged layer around particles which inhibit agglomeration. ...
The properties of silver nanoparticles (AgNPs) are affected by various parameters, making optimisation of their synthesis a laborious task. This optimisation is facilitated in this work by concurrent use of a T-junction microfluidic system and machine learning approach. The AgNPs are synthesized by reducing silver nitrate with tannic acid in the presence of trisodium citrate, which has a dual role in the reaction as reducing and stabilizing agent. The study uses a decision tree-guided design of experiment method for the size of AgNPs. The developed approach uses kinetic nucleation and growth constants derived from an independent set of experiments to account for chemistry of synthesis, the Reynolds number and the ratio of Dean number to Reynolds number to reveal effect of hydrodynamics and mixing within device and storage temperature to account for particle stability after collection. The obtained model was used to define a parameter space for additional experiments carried out to improve the model further. The numerical results illustrate that well-designed experiments can contribute more effectively to the development of different machine learning models (decision tree, random forest and XGBoost) as opposed to randomly added experiments.
... The bathochromic shift indicates an increase in particle size and a decrease in absorbance indicates the nanoparticles have changed in size to silver ions [32]. The existence of a widening peak in the 6th cycle nanoparticle spectrum also indicates that aggregation has occurred which is also characterized by the formation of sediment on organoleptic observations [33]. The instability of the silver nanoparticle suspension was also characterized by a decrease in the pH value of the silver nanoparticle suspension. ...
... Cit stabilizes the AgNPs by charge repulsion and is weakly bound to the silver core. PVP stabilizes the NPs sterically and is strongly bound to the core, being permeable to solutes and solvents [42,43]. ...
The combination of two or more agents capable of acting in synergy has been reported as a valuable tool to fight against pathogens. Silver nanoparticles (AgNPs) present a strong antimicrobial action, although their cytotoxicity for healthy cells at active concentrations is a major concern. Azoimidazole moieties exhibit interesting bioactivities, including antimicrobial activity. In this work, a class of recently described azoimidazoles with strong antifungal activity was conjugated with citrate or polyvinylpyrrolidone-stabilized AgNPs. Proton nuclear magnetic resonance was used to confirm the purity of the compounds before further tests and atomic absorption spectroscopy to verify the concentration of silver in the prepared dispersions. Other analytical techniques elucidate the morphology and stability of AgNPs and corresponding conjugates, namely ultraviolet–visible spectrophotometry, scanning transmission electron microscopy and dynamic light scattering analysis. The synergistic antimicrobial activity of the conjugates was assessed through a checkerboard assay against yeasts (Candida albicans and Candida krusei) and bacteria (Staphylococcus aureus and Escherichia coli). The conjugates showed improved antimicrobial activity against all microorganisms, in particular towards bacteria, with concentrations below their individual minimal inhibitory concentration (MIC). Furthermore, some combinations were found to be non-cytotoxic towards human HaCaT cells.
... Optimisation of the chemical synthesis process is a very labour-intensive, costly and time-consuming task because it includes multiple reagents and different independent experimental conditions including the types and concentrations of reactants, temperature, reactor design and mixing conditions. For example, the size of AgNPs strongly depends on both the type and concentration of stabilizing agent [2], [3], [4] and often depends on pH of the solution [5], [6], [7]. Ionic stabilizers such as citrate used in this study produce a charged layer around particles which inhibit agglomeration. ...
... Sun et al. also found peaks related to polysaccharide groups in an EPS FT-IR spectrum and they also found peaks around 400 and 900 cm -1 that could be attributed to phosphate in nucleic acids [32] . The same zone was attributed by Zeng et al. to phosphate or sulfate groups [32][33][34][35][36] . ...
Despite increasing interest in and use of nanoparticles (NP), the environmental consequences of using NP are poorly understood because most relevant studies have not taken the effects of natural coatings on NP into consideration. The aim of this study was to improve our understanding of the fates of NP in aquatic systems. The fates of silver NP (AgNP) capped with citrate and polyethylene glycol dispersed in ecotoxicological matrices in the presence of environmentally relevant components of natural water (humic substances and extracellular polymeric substances) were investigated. Interactions between AgNP and natural organic matter were evaluated by ultracentrifugation and electrophoretic mobility measurements to assess AgNP dissolution. Humic substances and extracellular polymeric substances both decreased the dissolution rate. The natural organic matter (humic substances and extracellular polymeric substances) provided conditions in which the medium stabilized the NP. The dissolution rate depended on the coating type (citrate or polyethylene glycol), dissolved organic carbon concentration, and particle concentration. The presence of algae and Daphnia affected AgNP conversion, demonstrating the value of research that takes environmentally relevant matrices into consideration. The results improve our understanding of the factors that affect the bioavailabilities of AgNP and therefore improve our ability to evaluate AgNP toxicity. Studies of other NP using the same strategy will improve our understanding of the fates of nanomaterials in the environment and biota.
Highlights
• Natural organic matter controls silver nanoparticle environmental dissolution/fate;
• Exopolysaccharides and aquatic humic substances both promote AgNP stabilization;
• Capping agents (citrate or polyethylene glycol) change the AgNP dissolution rate;
• AgNP behave differently when considering media for algae and Daphnia bioassays.
... The mechanisms associated with antibacterial action can be classified in two ways: the first one is the generation of reactive oxygen species (ROS) that has been previously related to the antimicrobial properties of silver compounds [10]. The most important ROS studied in the context of AgNPs are singlet oxygen, hydrogen peroxide, superoxide radical anion and hydroxyl radicals [10][11][12][13][14]. These reactive oxygen species can cause severe damage to DNA, RNA, lipids and proteins [14,15]. ...
Citation: Alarcon, R.; Walter, M.; Paez, M.; Azócar, M.I. Ostwald Ripening and Antibacterial Activity of Silver Nanoparticles Capped by Anti-Inflammatory Ligands. Nanomaterials 2023, 13, 428. Abstract: Silver nanoparticles (AgNPs) have been extensively studied during recent decades as antimicrobial agents. However, their stability and antibacterial activity over time have yet to be sufficiently studied. In this work, AgNPs were coated with different stabilizers (naproxen and diclofenac and 5-chlorosalicylic acid) in different concentrations. The suspensions of nanostructures were characterized by transmission electron microscopy, UV-Vis and FT-IR spectroscopic techniques. The antibacterial activity as a function of time was determined through microbiological studies against Staphylococcus aureus. The AgNPs show differences in stabilities when changing the coating agent and its concentration. This fact could be a consequence of the difference in the nature of the interaction between the stabilizer and the surface of the NPs, which were evaluated by FT-IR spectroscopy. In addition, an increase in the size of the nanoparticles was observed after 30 days, which could be related to an Ostwald maturation phenomenon. This result raises new questions about the role that stabilizers play on the surface of NPs, promoting size change in NPs. It is highly probable that the stabilizer functions as a growth controller of the NPs, thus determining an effect on their biological properties. Finally, the antibacterial activity was evaluated over time against the bacterium Staphylococcus aureus. The results showed that the protective or stabilizing agents can play an important role in the antibacterial capacity, the control of the size of the AgNPs and additionally in the stability over time.
Nanomaterials are the structural entities having one of the dimensions < 100 nm. Nanotechnology encompasses imaging, measuring, modelling, and manipulation of matter at nano dimensional level. Recent advancements in this field have brought to light the significant potential of nanoparticles (NPs) in a multitude of scientific areas. A variety of NPs have found their potential in several fields of biology, medicine, cosmetics etc. Still research scientists are investigating their potential in various other fields. In spite of numerous advantages resulting from the usability of NPs, several issues are arising related to their activities and unfavourable implications. Increasing applicability of these nano-sized entities has caused their discharge and subsequent accumulation into different ecosystems. Exposure to NPs may lead to a series of noxious effects on an organism. The toxic effects of NPs towards human health are governed by their shape and size, aspect ratio, surface charge, degree of agglomeration, density, surface and structural imperfections and dissolution rate. Prior knowledge of these distinctive properties of NPs along with their interactions with systems is imperative for the safer and wide usage of NPs. In other words, it is extremely enviable to verify the biocompatibility and distribution of nano materials prior to their utilization. This review article is envisioned to develop an intensive and extensive understanding of not only unforeseen but also unanticipated detrimental effects of nanomaterials on biological systems.
We encapsulated silver nanoplates (AgNPLs) into poly(lactic-co-glycolic) acid (PLGA) nanoparticles. The encapsulation stabilized the AgNPLs in a physiological environment and the antibacterial activity of the AgNPLs against planktonic bacteria was reduced. However, the PLGA nanoparticles encapsulating the AgNPLs were internalized into macrophages and showed antibacterial activity against intracellular bacteria. AgNPL-loaded PLGA nanoparticles are promising for treating intractable infectious diseases caused by bacteria-infecting macrophages.
Green combination of NPS has drawn in an incredible consideration on account of natural applications. In this work, bismuth oxide NPS (Bi2O3 NP) has been arranged by green amalgamation utilizing cocoa plants watery concentrate, the item was portrayed by X-beam diffraction, (UV-VIS) spectrophotometer, FTIR, Field Emission-Scanning Electron Microscopy Photoluminescence (PL), The antifungal activity of not set in stone against Candida albicans, the targets of this study were the green blend of bismuth oxide NPS utilizing fluid concentrate and antifungal action.
The synthesis of nanoparticles using biological molecules has become one of the current research areas due to the high toxic content, poor stability, and expensive production technologies of nanoparticles synthesized by physical and chemical technologies. With the approach called green synthesis, nanoparticles that do not contain toxic substances have been produced in a method that does not harm the environment and human health. The number of polyphenol compounds in the ethyl alcohol/water extract of propolis collected from the Muğla-Türkiye region was determined. The synthesis and characterization of silver nanoparticles were carried out using the ethyl alcohol/water extract of propolis. The descriptions of the synthesized nanoparticles were made using ultraviolet-visible absorption and attenuated total reflection-Fourier transform infrared. Scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction methods were used for morphological examinations. Which polyphenol compound in the propolis content is effective in the synthesis of nanosilver particles was investigated with a Gaussian 16 package program. The electronic properties of the compounds were obtained by density functional theory using boundary orbitals theory, molecular electrostatic surface potential, and nonlinear optical properties. Epigallocatechin gallate, Kaempferol, and Quercetin are effective in obtaining nano-Ag and can be used as organic optical material in technology.
Advantages of biosensors based on surface enhanced Raman scattering (SERS) rely on improved sensitivity and specificity, and suited reproducibility in detecting a target molecule that is localized in close proximity to a SERS-active surface. Herein, a comprehensive study on the realization of a SERS biosensor designed for detecting miRNA-183, a miRNA biomarker that is specific for chronic obstructive pulmonary disease (COPD), is presented. The used strategy exploits a signal-off mechanism by means of a labelled molecular beacon (MB) as the oligonucleotide biorecognition element immobilized on a 2D SERS substrate, based on spot-on silver nanowires (AgNWs) and a multi-well low volume cell. The MB was properly designed by following a dedicated protocol to recognize the chosen miRNA. A limit of detection down to femtomolar concentration (3 × 10-16 M) was achieved and the specificity of the biosensor was proved. Furthermore, the possibility to regenerate the sensing system through a simple procedure is shown: with regeneration by using HCl 1 mM, two detection cycles were performed with a good recovery of the initial MB signal (83%) and a reproducible signal after hybridization.
Glioblastomas (GBs) are one of the most aggressive and invasive intracranial cancers. Recently, it has been postulated that, among other factors, the hedgehog (HH) pathway may be a key factor in this phenomenon. Moreover, it has been reported that small-size silver nanoparticles (AgNPs) are characterized by a high cytotoxic effect towards GBs. However, their effect on the sonic hedgehog (SHH) pathway has never been demonstrated in any cancer cells. Therefore, the aim of the present study was to evaluate the impact of the anti-proliferative properties of 5-nm AgNPs on the SHH pathway in the GB cell line (U-87MG) in vitro. The results showed a time- and dose-dependent decrease in the metabolic activity in the U-87MG cells treated with AgNPs, with IC50 reaching 30.41 and 21.16 µg/mL after 24 h and 48 h, respectively, followed by an increase in the intracellular reactive oxygen species (ROS) level. The co-treatment of the cells with AgNPs and Robotnikinin (SHH inhibitor) abolished and/or strengthened the effect of AgNPs, especially on the SHH mRNA levels and on the PCNA, PTCH1, Gli1, and SUFU protein levels. Interestingly, no changes in the level of ERK1/2, Akt, and SRC kinase protein expression were detected, suggesting a direct impact of AgNPs and/or ROS on the inhibition of the canonical SHH pathway. However, more studies are needed due to the increase in the mTOR protein expression after the treatment of the cells with AgNPs, as in the Robotnikinin treatment. In conclusion, small-size AgNPs are able to inhibit the proliferation of GB cells in vitro by suppressing the canonical SHH pathway.
Magnetoelectric (ME) small‐scale robotic devices attract great interest from the scientific community due to their unique properties for biomedical applications. Here, novel ME nano hetero‐structures based on the biocompatible magnetostrictive MnFe2O4 (MFO) and ferroelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) are developed solely via the hydrothermal method for the first time. An increase in the temperature and duration of the hydrothermal synthesis results in increasing the size, improving the purity, and inducing morphology changes of MFO nanoparticles (NPs). A successful formation of a thin epitaxial BCZT‐shell with a 2–5 nm thickness is confirmed on the MFO NPs (77 ± 14 nm) preliminarily treated with oleic acid (OA) or polyvinylpyrrolidone (PVP), whereas no shell is revealed on the surface of pristine MFO NPs. High magnetization is revealed for the developed ME NPs based on PVP‐ and OA‐functionalized MFO NPs (18.68 ± 0.13 and 20.74 ± 0.22 emu g⁻¹, respectively). Moreover, ME NPs demonstrate 95% degradation of a model pollutant Rhodamine B within 2.5 h under an external AC magnetic field (150 mT, 100 Hz). Thus, the developed biocompatible core–shell ME NPs of MFO and BCZT can be considered as a promising tool for non‐invasive biomedical applications, environmental remediation, and hydrogen generation for renewable energy sources.
Importance of hospital environment in patient-care has been recognized widely in infection prevention and control. Inappropriate antibiotic use led to emergence of resistant strains that are difficult to treat with the available antibiotics. Progress in nanotechnology led to enhancement of nanoparticles with physicochemical characteristics and functionality that overcomes the constraints of common antimicrobials. Aim was to investigate effective antimicrobial role of Silver nanoparticle (Ag-NPs) against clinically important bacterial strains and observe effects of varying storage temperatures on Ag-NPs antimicrobial activity. Different concentrations of Ag-NPs were tested against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii using diffusion method. Zone of inhibition (ZOI) for each organism was directly proportional to concentration of Ag-NPs used. Mean ZOI values at different concentrations were significantly different for all organisms with p-value <0.001 for E. coli, S. aureus, P. aeruginosa and 0.004 for A. baumannii. Variation in storage temperature hardly showed any effects on the antimicrobial property of the Ag-NPs. Scanning electron microscopy (SEM) showed morphological and size variations in Ag-NPs exposed cells when compared to control strains, especially for S. aureus, E. coli and P. aeruginosa. Damaged cell membrane areas can be clearly distinguished in E. coli and P. aeruginosa thus suggesting bacterial membrane disruption. These finding can help design a larger study where Ag-NPs can be used in various medical instruments which are usually kept at room temperatures. Also, outcomes of this study may help in designing proper implants, prosthesis and equipment coated with minimum concentration of nanoparticles that might be considered safe for medical applications.
Water reclamation is the most effective way to continuously provide clean water to combat catastrophic global water scarcity. However, current technology for water purification is not conducive to sustainability due to the high energy consumption and negative environmental impact. Here, we introduce an innovative method by utilizing the hierarchical microstructure of bamboo for water purification. Natural bamboo was delignified followed by freeze-drying to obtain a bamboo aerogel with a porosity of 72.0%; then, the bamboo aerogel was coated with silver nanoparticles to form a hierarchical bamboo/silver nanoparticle composite. The scanning electron microscopy images and energy-dispersive X-ray spectroscopy results indicated that the silver nanoparticles were uniformly attached to the parenchyma cell surface. By physical adsorption and catalytic reduction, the bamboo/silver nanoparticle composite was able to degrade methylene blue by more than 96.7%, which is mainly attributed to the large specific surface area of the bamboo providing more space for the purification reaction. This composite can be potentially used for board applications with its high porosity, mechanical reliability, and sustainability.
Achieving high stability and excellent optical performance in complex environments is crucial for practical applications of magnetically responsive photonic crystals (MRPCs). It, however, remains a great challenge. This study demonstrates a polyphenol‐mediated strategy for synthesizing size‐controllable superparamagnetic magnetite (Fe3O4) colloid nanocrystal clusters (CNCs) that can be stably dispersed in various polar solvents to form MRPCs with brilliant structural colors for a long term. As tannic acid (TA) functions as a linker to robustly bind polyvinylpyrrolidone (PVP) chains to Fe3O4 surfaces, the MRPCs can maintain nearly constant diffraction wavelength and high reflectance for up to 4 years. The strong coordination between TA and Fe³⁺ inhibits crystal growth, ensuring the small primary crystal size and superparamagnetism of Fe3O4@TA‐PVP CNCs. Partial oxidation of TA accelerates the crystal nucleation and growth, reducing the overall CNC particle size, which can be utilized for controlling the particle size. Additionally, enhancing the dissolution of PVP before the solvothermal reaction improves the size monodispersity of the products, making the as‐constructed MRPCs ideal for practical applications in color display, sensors, anti‐counterfeiting, and camouflage. The Fe3O4@TA‐PVP CNCs with high stability and versatility for surface‐functionalization are also promising for magnetic resonance imaging, targeting drug delivery, recyclable catalysis, and magnetic nanomotors.
In this study, polymer (polyethylene glycol [PEG] and Chitosan)‐coated silver oxide nanoparticles (NPs) have been prepared by hydrothermal method. The polymer‐encapsulated NPs are characterized by materials‐related characterization techniques such as X‐Ray diffraction (XRD), scanning electron microscope (SEM), Ultraviolet–visible (UV–Vis), photoluminescence (PL), and Fourier‐transform infrared (FTIR) spectroscopy. The crystallite size of silver oxide NPs is 43.39 nm and reduces to 34.56 nm and 30.43 nm for PEG and Chitosan functionalized NPs, respectively. SEM micrographs show the spherical morphology of the synthesized nanomaterials with the grain size of pristine, PEG, and Chitosan functionalized silver oxide NPs as 60.9 ± 14.1, 70.9 ± 10.3, and 57.2 ± 7.8 nm, respectively. The band gap of silver oxide NPs increases upon polymer functionalization. PEGlyation of silver oxide NPs has enhanced its anticancer potential significantly against liver cancer cell line (HuH‐7), shows least cell viability, and IC 50 value is as low as 0.106 μg/mL and in the case of Chitosan coating 4.505 μg/mL. The antibacterial properties and biofilm inhibition are investigated against bacterial extracts of Escherichia coli and Staphylococcus aureus . The polymer‐coated silver oxide NPs have shown enhanced antibacterial potential against both S. aureus and E. coli. CAM assay is used to evaluate the wound‐healing ability of nanomaterials. Alginate gels incorporated with NPs have promoted wound healing. Our results revealed that the surface modification by PEG and Chitosan improved the therapeutic potential of silver oxide NPs.
Photoacoustic imaging (PAI) and imaging‐guided photothermal therapy (PTT) in the second near‐infrared window (NIR‐II, 1000–1700 nm) have received increasing attention owing to their advantages of greater penetration depth and higher signal‐to‐noise ratio. Plasmonic nanomaterials with tunable optical properties and strong light absorption provide an alternative to dye molecules, showing great prospects for phototheranostic applications. In this review, the research progress in principally modulating the optical properties of plasmonic nanomaterials, especially affecting parameters such as size, morphology, and surface chemical modification, is introduced. The commonly used plasmonic nanomaterials in the NIR‐II window, including noble metals, semiconductors, and heterostructures, are then summarized. In addition, the biomedical applications of these NIR‐II plasmonic nanomaterials for PAI and PTT in phototheranostics are highlighted. Finally, the perspectives and challenges for advancing plasmonic nanomaterials for practical use and clinical translation are discussed.
The widespread applications of silver nanoparticles (AgNPs) throughout our daily lives have raised concerns regarding their environmental health and safety (EHS). Despite an increasing number of studies focused on the EHS impacts of AgNPs, there remain significant knowledge gaps with respect to their potential health impacts on susceptible populations, such as lactating mothers and infants. Herein, we aimed to investigate the deleterious effects of AgNPs with different sizes (20 and 40 nm) and surface coatings (PVP and BPEI) on maternal mice and their offspring following lactation exposure at doses of 20, 100 and 400 μg/kg body weight. We discovered that AgNPs could accumulate in the maternal mammary glands and disrupt the epithelial barrier in a dose-dependent manner. Notably, BPEI-coated AgNPs caused more damage to the mammary glands than PVP-coated particles. Importantly, we observed that, while AgNPs were distributed throughout the blood and main tissues, they were particularly enriched in the brains of breastfed offspring after maternal exposure during lactation, exhibiting exposure dosage- and particle coating-dependent patterns. Compared to PVP-coated nanoparticles, BPEI-coated AgNPs were more readily transferred to the offspring, possibly due to their enhanced deposition in maternal mammary glands. Moreover, we observed reduced body weight, blood cell toxicity, and tissue injuries in breastfed offspring whose dams received AgNPs. As a whole, these results reveal that maternal exposure to AgNPs results in the translocation of AgNPs into offspring via breastfeeding, inducing developmental impairments in these breastfed offspring. This study provides important new insights into the EHS impacts of AgNP consumption during lactation.
Optical Properties, Characterisation techniques for nanoparticles, Methods for the production of silver nanoparticles, UV-Vis spectrophotometry, X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Dynamic light scattering (DLS), Ager electron spectroscopy, Low-energy ion scattering (LEIS). Abstract: Silver nanoparticles with sizes between 1 and 100 nanometer are frequently used in industries such as catalysis, electronics, and photonics. They have special qualities like optical, electrical, and magnetic characteristics that can be used as antimicrobial, biosensor textile, cosmetics, composite fibres, and electronic components, as well as to extend the shelf life of food substances. The primary goal of this review was to concentrate on recent developments in silver nanoparticle formulation techniques as well as potential future applications. The potential for biological uses of silver nanoparticles is extremely significant. A variety of physical, chemical, and biological methods have been used to create and stabilise silver nanoparticles. Many techniques, such as chemical simplicity with various organic and inorganic degrading agents, physicochemical reduction, electrochemical processes, and radiolysis, are used to create silver nanoparticles. The most often utilised component in all nanotechnology products is silver nanoparticles, according to manufacturers. To extend the shelf life, they can be added to food packaging polymers. The current review focuses on various synthesis methods and specifics of silver nanoparticles employed as drug delivery systems, antibacterial activity, toxicity, recent developments, and future considerations.
One of the most important processes in the fight against current and future pandemics is the rapid diagnosis and initiation of treatment of viruses in humans. Currently available viral diagnostic methods detect only known pathogens, which comprise a small number of virus strains. In addition, identifying viral genomes is challenging due to low viral abundance and possible contamination by host nucleic acids. To ensure the distinction between the infected and non-infected people and predict the outbreak of disease, alternative approaches should be considered. In the ongoing hunt for new developing tests and diagnostic kits with high selectivity and sensitivity, plasmonic platforms, which control light in subwavelength volumes, have opened up exciting prospects for biosensing applications. They can identify particular viruses in a cost-effective, sensitive, label-free, rapid, and reproducible way due to their tunable plasmonic properties. In particular, plasmonic-assisted virus detection platforms can be achieved by various approaches, including propagating surface and localized plasmon resonances, as well as surface-enhanced Raman spectroscopy. In this review, we discuss both the fundamental principles governing a plasmonic biosensor and prospects for achieving improved sensor performance. We highlight several nanostructure schemes to combat virus-related diseases. We also examine the technological limitations and challenges of plasmonic-based biosensing, such as reducing the overall cost and handling of complex biological samples. Finally, we provide a future perspective for opportunities to improve plasmonic-based approaches to increase their impact on global health issues.
Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR‐independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure‐activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano‐microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.
Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR‐independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure‐activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano‐microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.
Background
The potential for nanoparticles to cause harm to human health and the environment is correlated with their biodurability in the human body and persistence in the environment. Dissolution testing serves to predict biodurability and nanoparticle environmental persistence. In this study, dissolution testing using the continuous flow through system was used to investigate the biodurability and persistence of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), and titanium dioxide nanoparticles (TiO2 NPs) in five different simulated biological fluids and two synthetic environmental media to predict their behaviour in real life situations.
Results
The level of dissolved nanoparticles in simulated acidic media was more and higher in magnitude compared to that dissolved in simulated alkaline media. The results obtained via the continuous flow through dissolution system also displayed very significant dissolution rates. For TiO2 NPs the calculated half-times were in the range of 13–14 days, followed by AuNPs ranging between 4–12 days, significantly longer if compared to the half-times of AgNPs ranging between 2–7 days. AuNPs and TiO2 NPs were characterized by low dissolution rates therefore are expected to be (bio)durable in physiological surroundings and persistent in the environment thus, they might impose long-term effects on humans and the environment. In contrast, AgNPs have high dissolution rates and not (bio)durable and hence may cause short-term effects.
Conclusion
The results suggest a hierarchy of biodurability and persistence of TiO2 NPs > AuNPs > AgNPs. It is recommended that nanoparticle product developers should follow the test guidelines stipulated by the OECD to ensure product safety for use before it is taken to the market.
The colloidal properties of engineered nanoparticles directly affect their use in a wide variety of applications and also control their environmental fate and mobility. The colloidal stability of engineered nanoparticles depends on their physicochemical properties within the given aqueous medium and is ultimately reflected in the particles' aggregation and deposition behaviour. This review presents some of the key experimental methods that are currently used to probe colloidal properties and quantify engineered nanoparticle stability in water. Case studies from fullerene C60 nanoparticles and multi-walled carbon nanotubes illustrate how the characterisation and measurement methods are used to understand and predict nanoparticle fate in aquatic systems. Consideration of the comparisons between these two classes of carbon-based nanoparticles provides useful insights into some major current knowledge gaps while also revealing clues about needed future developments. Key issues to be resolved relate to the nature of near-range surface forces and the origins of surface charge, particularly for the reportedly unmodified or 'pure' carbon-based nanoparticles.
The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.
Ecotoxicology research is using many methods for engineered nanomaterials (ENMs), but the collective experience from researchers has not been documented. This paper reports the practical issues for working with ENMs and suggests nano-specific modifications to protocols. The review considers generic practical issues, as well as specific issues for aquatic tests, marine grazers, soil organisms, and bioaccumulation studies. Current procedures for cleaning glassware are adequate, but electrodes are problematic. The maintenance of exposure concentration is challenging, but can be achieved with some ENMs. The need to characterize the media during experiments is identified, but rapid analytical methods are not available to do this. The use of sonication and natural/synthetic dispersants are discussed. Nano-specific biological endpoints may be developed for a tiered monitoring scheme to diagnose ENM exposure or effect. A case study of the algal growth test highlights many small deviations in current regulatory test protocols that are allowed (shaking, lighting, mixing methods), but these should be standardized for ENMs. Invertebrate (Daphnia) tests should account for mechanical toxicity of ENMs. Fish tests should consider semistatic exposure to minimize wastewater and animal husbandry. The inclusion of a benthic test is recommended for the base set of ecotoxicity tests with ENMs. The sensitivity of soil tests needs to be increased for ENMs and shortened for logistics reasons; improvements include using Caenorhabditis elegans, aquatic media, and metabolism endpoints in the plant growth tests. The existing bioaccumulation tests are conceptually flawed and require considerable modification, or a new test, to work for ENMs. Overall, most methodologies need some amendments, and recommendations are made to assist researchers.
This review summarises and evaluates the present knowledge on the behaviour, the biological effects and the routes of uptake of silver nanoparticles (Ag NPs) to organisms, with considerations on the nanoparticle physicochemistry in the ecotoxicity testing systems used. Different types of Ag NP syntheses, characterisation techniques and predicted current and future concentrations in the environment are also outlined. Rapid progress in this area has been made over the last few years, but there is still a critical lack of understanding of the need for characterisation and synthesis in environmental and ecotoxicological studies. Concentration and form of nanomaterials in the environment are difficult to quantify and methodological progress is needed, although sophisticated exposure models show that predicted environmental concentrations (PECs) for Ag NPs in different environmental compartments are at the range of ng L(-1) to mg kg(-1). The ecotoxicological literature shows that concentrations of Ag NPs below the current and future PECs, as low as just a few ng L(-1), can affect prokaryotes, invertebrates and fish indicating a significant potential, though poorly characterised, risk to the environment. Mechanisms of toxicity are still poorly understood although it seems clear that in some cases nanoscale specific properties may cause biouptake and toxicity over and above that caused by the dissolved Ag ion. This review concludes with a set of recommendations for the advancement of understanding of the role of nanoscale silver in environmental and ecotoxicological research.
Experimental conditions that mimic likely scenarios of manufactured nanomaterials (MNs) introduction to aquatic systems were used to assessthe effect of nanoparticle dispersion/solubility and water chemical composition on MN-toxicity. Aqueous suspensions of fullerenes (C60), nanosilver (nAg), and nanocopper (nCu) were prepared in both deionized water and filtered (0.45 microm) natural river water samples collected from the Suwannee River basin, to emphasize differences in dissolved organic carbon (DOC) concentrations and solution ionic strengths (I). Two toxicity tests, the Ceriodaphnia dubia and MetPLATE bioassays were used. Results obtained from exposure studies show that water chemistry affects the suspension/solubility of MNs as well as the particle size distribution, resulting in a wide range of biological responses depending on the type of toxicity test used. Under experimental conditions used in this study, C60 exhibited no toxicity even when suspended concentrations exceeded 3 mg L(-1). MetPLATE results showed that the toxicity of aqueous suspensions of nCu tends to increase with increasing DOC concentrations, while increasing I reduces nCu toxicity. The use of the aquatic invertebrate C. dubia on the other hand showed a tendency for decreased mortality with increasing DOC and I. MetPLATE results for nAg showed decreasing trends in toxicity with increasing DOC concentrations and I. However, C. dubia exhibited contrasting biological responses, in that increasing DOC concentrations reduced toxicity, while the latter increased with increasing I. Overall, our results show that laboratory experiments that use DI-water and drastic MN-suspension methods may not be realistic as MN-dispersion and suspension in natural waters vary significantly with water chemistry and the reactivity of MNs.
The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.
The level of production of nanoparticles will inevitably lead to their appearance in air, water, soils, and organisms. A theoretical framework that relates properties of nanoparticles to their biological effects is needed to identify possible risks to human health and the environment. This paper considers the properties of dispersed metallic nanoparticles and highlights the relationship between the chemical stability of these nanoparticles and their in vitro toxicity. Analysis of published data suggests that chemically stable metallic nanoparticles have no significant cellular toxicity, whereas nanoparticles able to be oxidized, reduced or dissolved are cytotoxic and even genotoxic for cellular organisms.
Metal oxide nanoparticles are finding increasing application in various commercial products, leading to concerns for their environmental fate and potential toxicity. It is generally assumed that nanoparticles will persist as small particles in aquatic systems and that their bioavailability could be significantly greater than that of larger particles. The current study using nanoparticulate ZnO (ca. 30 nm) has shown that this is not always so. Particle characterization using transmission electron microscopy and dynamic light scattering techniques showed that particle aggregation is significant in a freshwater system, resulting in flocs ranging from several hundred nanometers to several microns. Chemical investigations using equilibrium dialysis demonstrated rapid dissolution of ZnO nanoparticles in a freshwater medium (pH 7.6), with a saturation solubility in the milligram per liter range, similar to that of bulk ZnO. Toxicity experiments using the freshwater alga Pseudokirchneriella subcapitata revealed comparable toxicity for nanoparticulate ZnO, bulk ZnO, and ZnCl2, with a 72-h IC50 value near 60 microg Zn/ L, attributable solely to dissolved zinc. Care therefore needs to be taken in toxicity testing in ascribing toxicity to nanoparticles per se when the effects may be related, at least in part, to simple solubility.
The emerging literature on the ecotoxicity of nanoparticles and nanomaterials is summarised, then the fundamental physico-chemistry that governs particle behaviour is explained in an ecotoxicological context. Techniques for measuring nanoparticles in various biological and chemical matrices are also outlined. The emerging ecotoxicological literature shows toxic effects on fish and invertebrates, often at low mg l(-1) concentrations of nanoparticles. However, data on bacteria, plants, and terrestrial species are particularly lacking at present. Initial data suggest that at least some manufactured nanoparticles may interact with other contaminants, influencing their ecotoxicity. Particle behaviour is influenced by particle size, shape, surface charge, and the presence of other materials in the environment. Nanoparticles tend to aggregate in hard water and seawater, and are greatly influenced by the specific type of organic matter or other natural particles (colloids) present in freshwater. The state of dispersion will alter ecotoxicity, but many abiotic factors that influence this, such as pH, salinity, and the presence of organic matter remain to be systematically investigated as part of ecotoxicological studies. Concentrations of manufactured nanoparticles have rarely been measured in the environment to date. Various techniques are available to characterise nanoparticles for exposure and dosimetry, although each of these methods has advantages and disadvantages for the ecotoxicologist. We conclude with a consideration of implications for environmental risk assessment of manufactured nanoparticles.
The level of production of nanoparticles will inevitably lead to their appearance in air, water, soils, and organisms. A theoretical framework that relates properties of nanoparticles to their biological effects is needed to identify possible risks to human health and the environment. This paper considers the properties of dispersed metallic nanoparticles and highlights the relationship between the chemical stability of these nanoparticles and their in vitro toxicity. Analysis of published data suggests that chemically stable metallic nanoparticles have no significant cellular toxicity, whereas nanoparticles able to be oxidized, reduced or dissolved are cytotoxic and even genotoxic for cellular organisms.
A laboratory experiment introduces students to a unique property of a nanomaterial: the intense yellow color exhibited by silver nanoparticles compared to ionic or bulk silver. Students synthesize colloidal silver, estimate particle size using visible spectroscopy, and study aggregation and its prevention by addition of a polymer stabilizer. This experiment, intended as a laboratory activity for general chemistry, introduces students to nanotechnology while reinforcing topics such as redox chemistry, limiting and excess reactants, spectroscopy, and atomic size. The experiment requires dilute solutions and simple equipment such as the Spectronic-20 spectrophotometer and a magnetic stir plate. The reaction used for the synthesis of silver nanoparticles is the borohydride reduction of silver nitrate. The method produces 12 ± 2 nm particles and plasmon absorbance near 400 nm. In developing the experiment, transmission electron microscope (TEM) images were used to determine particle size; however, TEM is not involved in the student experiment. The experimental design is discussed, including the choice of concentrations of reactants, the relationship of particle size to optical properties, as well as a discussion of aggregation and stabilizers. The experiment was tested on laboratory classes of science majors. Keywords (Audience): Second-Year UndergraduateKeywords (Domain): Laboratory InstructionKeywords (Subject): Colloids
The study of nanometer and subnanometer colloidal metal particles in aqueous solution complements the investigation of small particles in molecular beams, frozen solutions, and inorganic clusters. The electronic properties of the metal particles are changed by surface modification, for example by chemisorption of a nucleophilic molecule or by deposition of a second metal. The resulting changes in the chemical, photochemical, and optical properties are discussed. Methods are described which enable one to store excess electrons or positive holes on the particles in a controlled manner and to investigate the accompanying changes in the optical properties. Metal particles carrying excess electrons initiate electrochemical reactions such as the reduction of water or the deposition of metals. Concentric bimetallic and trimetallic particles can be synthesized this way. The transition from the atom to the metal can be studied by pulse radiolysis: a known concentration of atoms is generated by a pulse and the development of the metal absorption spectrum is then recorded as a function of time as the atoms coalesce to yield larger particles. It is often observed that the absorption spectrum of the metal is reached after only a few coalescence steps, i.e. at agglomeration numbers of about 10. In the case of silver, two ''magic'' clusters which are not metallic and having long lifetimes (100 s and 15 min) are observed during the coalescence. These clusters have ''giant'' absorption bands at wavelengths distinctly shorter than that of the 380-nm plasmon band of metallic silver particles. The clusters live for hours and days in the presence of polyanions. They have reducing properties and also react eagerly with nucleophilic reagents. They can be fragmented upon illumination and photoemit electrons with quantum yields greater than 0.1. The dependence of the standard redox potential on particle size is also discussed. The atom-to-metal transition manifests itself also in the colloid chemical properties of metal particles (transition from complex formation with anions of oligomeric clusters to double layer formation around larger particles).
Single-crystal cubes and tetrahedrons of silver with truncated corners/edges have been prepared for the first time in high yields by reducing silver nitrate with ethylene glycol heated to 148 °C in the presence of poly(vinyl pyrrolidone) and a trace amount of sodium chloride. These nanoparticles were relatively monodisperse in size and shape, and their dimensions could be readily controlled in the range of 20 to 80 nm by varying the reaction time and other experimental parameters. We propose that the defects inherent in twinned nuclei of silver led to their selective etching and dissolution by chloride and oxygen (from air), leaving only the single crystalline ones to grow into nanoscale cubes and tetrahedrons.
The sculpturing effect of chloride ions on the shape transformation of silver nanoparticles is presented. UV−vis spectroscopy and transmission electron microscopy (TEM) were used to monitor the evolution of silver nanoplates. Cl− can etch the corners and side faces of the silver nanoprism, and the resulting nanoparticles are disk-like in shape. The dissolved silver atoms would aggregate to form small silver clusters, which were stabilized by the Cl− and citrate ions. The facet-selective etching effect of Cl− is mainly attributed to the surface energy difference of each face of the nanoplate. The thickness of the nanodisk increased during the etching process because of the redeposition of sliver clusters on the {111} planes. The prepared nanodisk also gave rise to high SERS intensity of the probing molecule.
In this first systematic study, we describe the influence of various surfactants and polymers on aggregation stability and antibacterial activity of silver nanoparticles (NPs) prepared by a modified Tollens process. The surfactant/polymer stabilizing effect was monitored using the newly established method based on a titration of the aqueous dispersion of the silver NPs by aqueous solution of poly(diallyldimethylammonium) chloride (PDDA). The aggregation process was evaluated by the dynamic light scattering (DLS) and UV/vis spectra measurements and finally confirmed by TEM. Among all of the investigated modifiers, two surfactants (sodium dodecyl sulfate-SDS and polyoxyethylenesorbitane monooleate-Tween 80) and one polymer (polyvinylpyrrolidone-PVP 360) exhibit superior stabilization of the silver NP dispersions against the process of aggregation. The differences in the stabilization ability of various tested substances are discussed with respect to their structure and possible mechanism of the surface interaction with the NPs. The antibacterial activity of the modified silver NPs was significantly enhanced especially when modified by SDS where the minimum inhibition concentration (MIC) decreased under the “magical value” of 1 μg·mL-1. A correlation was found between the aggregation stability and enhanced antibacterial activity in the system of the silver NPs modified by SDS, Tween 80, and high molecular polymer PVP 360.
The environmental and health impacts of nanomaterials are becoming important topics of research in recent years. The unique advantages offered by these nanomaterials in wide range of applications cannot be realized until these concerns are resolved. Among all the nanomaterials, Ag nanoparticles, due to their existing extensive uses in commercial products, demand immediate attention. Since the nanoparticle suspensions will be exposed to environmental conditions different from a research lab setting, many factors, including light, temperature, salinity, etc., are suspected to affect the stability of the nanoparticle and also their toxicity. In this study, we examined the effect of sunlight on the stability and toxicity of 6 and 25 nm Ag nanoparticles coated with gum arabic (GA) and polyvinylpyrrolidone (PVP). Under sunlight irradiation, all of these nanoparticles irreversibly aggregated to different degrees depending on the surface coating. The UV content of the sunlight is identified to be the driving force of nanoparticle aggregation, and the strong oscillating dipole−dipole interaction is believed to be the origin of the destabilization. Toxicity examinations of the nanoparticles to a wetland plant, Lolium multiflorum, indicate that their toxicity is greatly reduced after sunlight irradiation.
A laboratory experiment introduces students to a unique property of a nanomaterial: the intense yellow color exhibited by silver nanoparticles compared to ionic or bulk silver. Students synthesize colloidal silver, estimate particle size using visible spectroscopy, and study aggregation and its prevention by addition of a polymer stabilizer. This experiment, intended as a laboratory activity for general chemistry, introduces students to nanotechnology while reinforcing topics such as redox chemistry, limiting and excess reactants, spectroscopy, and atomic size. The experiment requires dilute solutions and simple equipment such as the Spectronic-20 spectrophotometer and a magnetic stir plate. The reaction used for the synthesis of silver nanoparticles is the borohydride reduction of silver nitrate. The method produces 12 ± 2 nm particles and plasmon absorbance near 400 nm. In developing the experiment, transmission electron microscope (TEM) images were used to determine particle size; however, TEM is not involved in the student experiment. The experimental design is discussed, including the choice of concentrations of reactants, the relationship of particle size to optical properties, as well as a discussion of aggregation and stabilizers. The experiment was tested on laboratory classes of science majors. Keywords (Audience): Second-Year Undergraduate
In the present study, we report the preparation of silver nanoparticles in the range of 10–15 nm with increased stability and enhanced anti-bacterial potency. The morphology of the nanoparticles was characterized by transmission electron microscopy. The antibacterial effect of silver nanoparticles used in this study was found to be far more potent than that described in the earlier reports. This effect was dose dependent and was more pronounced against gram-negative bacteria than gram-positive organisms. Although bacterial cell lysis could be one of the reasons for the observed antibacterial property, nanoparticles also modulated the phosphotyrosine profile of putative bacterial peptides, which could thus affect bacterial signal transduction and inhibit the growth of the organisms.
Silver nanoparticles (AgNPs) are currently being very widely used in industry, mainly because of their anti-bacterial properties, with applications in many areas. Once released into the environment, the mobility, bioavailability, and toxicity of AgNPs in any ecosystem are dominated by colloidal stability. There have been studies on the stability or the aggregation of various nanoparticles (NPs) under a range of environmental conditions, but there is little information on fully characterised AgNPs in media used in (eco)toxicity studies. In this study, monodisperse 7, 10 and 20 nm citrate-stabilised AgNPs were synthesised, characterised and then fractionated and sized by flow field-flow fractionation (FFF) and measured with dynamic light scattering (DLS) in different dilutions of the media recommended by OECD for Daphnia magna (water flea) toxicity testing. Stability of NPs was assessed over 24 h, and less so over 21 days, similar time periods to the OECD acute and chronic toxicity tests for D. magna. All particles aggregated quickly in the media with high ionic strength (media1), resulting in a loss of colour from the solution. The size of particles could be measured by DLS in most cases after 24h, although a fractogram by FFF could not be obtained due to aggregation and polydispersity of the sample. After diluting the media by a factor of 2, 5 or 10, aggregation was reduced, although the smallest NPs were unstable under all media conditions. Media diluted up to 10-fold in the absence of AgNPs did not induce any loss of mobility or fecundity in D. magna. These results confirm that standard OECD media causes aggregation of AgNPs, which result in changes in organism exposure levels and the nature of the exposed particles compared to exposure to fully dispersed particles. Setting aside questions of dose metrics, significant and substantial reduction in concentration over exposure period suggests that literature data are in the main improperly interpreted and nanoparticles are likely to have far greater biological effects than suggested thus far by poorly controlled exposures. We recommend that the standard OECD media is diluted by a factor of ca. 10 for use with these NPs and this test media, which reduces AgNP aggregation without affecting the viability of the text organism.
Manufactured nanomaterials (MNMs) are rapidly being incorporated into a wide variety of commercial products with significant potential for environmental release, which calls for eco-responsible design and disposal of nanoenabled products. Critical research needs to advance this urgent priority include (1) structure-activity relationships to predict functional stability and chemistry of MNMs in the environment and to discern properties that increase their bioavailability, bioaccumulation, and toxicity; (2) standardized protocols to assess MNM bioavailability, trophic transfer, and sublethal effects; and (3) validated multiphase fate and transport models that consider various release scenarios and predict the form and concentration of MNMs at the point of exposure. These efforts would greatly benefit from the development of robust analytical techniques to characterize and to track MNMs in the environment and to validate models and from shared reference MNM libraries.
Although silver nanoparticles are being exploited widely in antimicrobial applications, the mechanisms underlying silver nanoparticle antimicrobial properties in environmentally relevant media are not fully understood. The latter point is critical for understanding potential environmental impacts of silver nanoparticles. The aim of this study was to elucidate the influence of inorganic aquatic chemistry on silver nanoparticle stability (aggregation, dissolution, reprecipitation) and bacterial viability. A synthetic "fresh water" matrix was prepared comprising various combinations of cations and anions while maintaining a fixed ionic strength. Aggregation and dissolution of silver nanoparticles was influenced by electrolyte composition; experimentally determined ionic silver concentrations were about half that predicted from a thermodynamic model and about 1000 times lower than the maximum dispersed silver nanoparticle concentration. Antibacterial activity of silver nanoparticles was much lower than Ag(+) ions when compared on the basis of total mass added; however, the actual concentrations of dissolved silver were the same regardless of how silver was introduced. Bacterial inactivation also depended on bacteria cell type (Gram-positive/negative) as well as the hardness and alkalinity of the suspending media. These simple, but systematic studies--enabled by high-throughput screening--reveal the inherent complexity associated with understanding silver nanoparticle antibacterial efficacy as well as potential environmental impacts of silver nanoparticles.
In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 micro Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.
Many important aspects of nanosilver behavior are influenced by the ionic activity associated with the particle suspension, including antibacterial potency, eukaryotic toxicity, environmental release, and particle persistence.The present study synthesizes pure, ion-free, citrate-stabilized nanosilver (nAg) colloids as model systems, and measures their time-dependent release of dissolved silver using centrifugal ultrafiltration and atomic absorption spectroscopy. Ion release is shown to be a cooperative oxidation process requiring both dissolved dioxygen and protons. It produces peroxide intermediates, and proceeds to complete reactive dissolution under some conditions. Ion release rates increase with temperature in the range 0-37 °C, and decrease with increasing pH or addition of humic or fulvic acids. Sea salts have only a minor effect on dissolved silver release. Silver nanoparticle surfaces can adsorb Ag(+), so even simple colloids contain three forms of silver: Ag(0) solids, free Ag(+) or its complexes, and surface-adsorbed Ag(+). Both thermodynamic analysis and kinetic measurements indicate that Ag(0) nanoparticles will not be persistent in realistic environmental compartments containing dissolved oxygen. An empirical kinetic law is proposed that reproduces the observed effects of dissolution time, pH, humic/fulvic acid content, and temperature observed here in the low range of nanosilver concentration most relevant for the environment.
Background:
Most recently, renewed interest has arisen in manufactured silver nanomaterials because of their unusually enhanced physicochemical properties and biological activities compared to the bulk parent materials. A wide range of applications has emerged in consumer products ranging from disinfecting medical devices and home appliances to water treatment. Because the hypothesized mechanisms that govern the fate and transport of bulk materials may not directly apply to materials at the nanoscale, there are great concerns in the regulatory and research communities about potential environmental impacts associated with the use of silver nanoparticles. In particular, the unlimited combinations of properties emerging from the syntheses and applications of silver nanoparticles are presenting an urgent need to document the predominant salt precursors, reducing agents and stabilizing agents utilized in the synthesis processes of silver nanoparticles to guide the massive efforts required for environmental risk assessment and management.
Objectives:
The primary objective of this study is to present an evidence-based environmental perspective of silver nanoparticle properties in syntheses and applications. The following specific aims are designed to achieve the study objective: Aim 1--to document the salt precursors and agents utilized in synthesizing silver nanoparticles; Aim 2--to determine the characteristics of silver nanoparticles currently in use in the scientific literature when integrated in polymer matrices to form nanocomposites and combined with other metal nanoparticles to form bimetallic nanoparticles; Aim 3--to provide a summary of the morphology of silver nanoparticles; and (4) Aim 4--to provide an environmental perspective of the evidence presented in Aims 1 to 3.
Methods:
A comprehensive electronic search of scientific databases was conducted in support of the study objectives. Specific inclusion criteria were applied to gather the most pertinent research articles. Data and information extraction relied on the type of synthesis methods, that is, synthesized silver nanoparticles in general and specific applications, nanocomposites, and bimetallic techniques. The following items were gathered for: type of silver salt, solvent, reducing agent, stabilizing agent, size, and type of application/nanocomposite/bimetallic, and template (for nanocomposites). The description of evidence was presented in tabular format. The critical appraisal was analyzed in graphical format and discussed.
Results:
An analysis of the scientific literature suggests that most synthesis processes produce spherical silver nanoparticles with less than 20nm diameter. Silver nanoparticles are often synthesized via reduction of AgNO(3), dissolution in water, and utilization of reductants also acting as capping or stabilizing agents for the control of particle size to ensure a relatively stable suspension. Two of the most commonly used reductants and stabilizing agents are NaBH(4) and citrate which yield particles with a negative surface charge over the environmental pH range (3-10). The environmental perspectives of these parameters are discussed.
Concluding remarks:
It is expected that the antibacterial property of bulk silver is carried over and perhaps enhanced, to silver nanoparticles. Therefore, when one examines the environmental issues associated with the manufacture and use of silver nanoparticle-based products, the antibacterial effects should always be taken into account particularly at the different stages of the product lifecycle. Currently, there are two arguments in the scientific literature about the mechanisms of antimicrobial properties of silver nanoparticles as they relate to colloidal silver particles and inonic silver. Methodologies of risk assessment and control have to account for both arguments.
NanoImpactNet is a European Commission Framework Programme 7 (FP7) funded project that provides a forum for the discussion of current opinions on nanomaterials in relation to human and environmental issues. In September 2008, in Zurich, a NanoImpactNet environmental workshop focused on three key questions: 1. What properties should be characterised for nanomaterials used in environmental and ecotoxicology studies? 2. What reference materials should be developed for use in environmental and ecotoxicological studies? 3. Is it possible to group different nanomaterials into categories for consideration in environmental studies? Such questions have been, at least partially, addressed by other projects/workshops especially in relation to human health effects. Such projects provide a useful basis on which this workshop was based, but in this particular case these questions were reformulated in order to focus specifically on environmental studies. The workshop participants, through a series of discussion and reflection sessions, generated the conclusions listed below. The physicochemical characterisation information identified as important for environmental studies included measures of aggregation/agglomeration/dispersability, size, dissolution (solubility), surface area, surface charge, surface chemistry/composition, with the assumption that chemical composition would already be known. There is a need to have test materials for ecotoxicology, and several substances are potentially useful, including TiO(2) nanoparticles, polystyrene beads labelled with fluorescent dyes, and silver nanoparticles. Some of these test materials could then be developed into certified reference materials over time. No clear consensus was reached regarding the classification of nanomaterials into categories to aid environmental studies, except that a chemistry-based classification system was a reasonable starting point, with some modifications. It was suggested, that additional work may be required to derive criteria that can be used to generate such categories, that would also include aspects of the material structure and physical behaviour.
Silver nanoparticles (Ag NPs) are widely used as antibacterial agents. This antibacterial property carries with it a potential environmental risk once these NPs are discharged into the environment. This study investigated the impact on Pseudomonas fluorescens over a 24 h exposure of well characterized Ag NPs at pH values of 6-9, in the presence and absence of Suwannee River humic acids (SRHA). Ag NPs were characterized by size, aggregation, morphology, dissolution, and surface properties under all conditions. Solubility was low (less than 2%) for all Ag NP concentrations (2-2000 ppb) and under all conditions was less than 40 ppb (0.38 microM). SRHA caused a partial disaggregation of Ag NP aggregates by nanoscale film formation, with individual NPs stabilized by charge and entropically driven steric effects. Dissolved Ag reduced bacterial growth entirely at 2000 ppb (19 microM) under all conditions and adversely affected growth at 200 ppb (1.9 microM) under some conditions, indicating some toxicity. The Ag NPs showed similar toxicity at 2000 ppb (19 microM) in the absence of SRHA and at pH 9 only i.e. SRHA mitigated bactericidal action. Solubility and interactions with SRHA indicate that there was a specific nanoparticle effect which could not be explained by the effect of dissolved Ag.
Silver nanoparticles (Ag NPs) are becoming increasingly popular as antimicrobial agents in consumer goods with consequent risk to environmental health from discharges. Environmentally relevant fate and transport investigations are limited but essential to gain understanding towards bioavailability and toxicology. In this study, monodisperse 15nm citrate-stabilised Ag NPs were synthesised, characterised and then fractionated by flow field-flow fractionation (FlFFF) at environmentally relevant conditions (pH 5 or 8, presence of natural organic macromolecules (NOM) and presence of sodium or calcium). At low ionic strength, Ag NPs particle size increased as pH increased from 5 to 8. However, changing the ionic strength from 10(-3) to 10(-2)M Na increased instability of the Ag NPs, and loss of peak at pH 5 but in the presence of humic substance (HS), a reduction in NP size was seen, most likely due to a reduction in the diffuse layer. The presence of Ca(2+) ions, at the higher ionic strengths caused complete loss of the solution Ag NPs with or without HS, most likely due to aggregation. At the lower Ca(2+) ionic strength the Ag NPs were still unstable, but again, in the presence of HS the NPs were largely dispersed. The presence of HS improved stability of Ag NPs under these conditions by forming a surface coating resulting in both steric and charge stabilisation. This work implies that Ag NPs could have long residence times in aquatic systems in the presence of HS potentially resulting in increased bioavailability.
Thiol-modified poly(ethylene glycol) (mPEG-SH) has been used to replace standard capping agents from the surfaces of gold nanoparticles with different sizes and shapes. Upon PEG stabilization, the nanoparticles can be transferred into ethanol, where silica can be directly grown on the particle surfaces through the standard Stober process. The obtained silica shells are uniform and homogeneous, and the method allows a high degree of control over shell thickness for any particle size and shape. Additionally, Raman-active molecules can be readily incorporated within the composite nanoparticles during silica growth so that SERS/SERRS-encoded nanoparticles can be fabricated containing a variety of tags, thereby envisaging multiplexing capability.
Metallic nanoparticles are among the most widely used types of engineered nanomaterials; however, little is known about their environmental fate and effects. To assess potential environmental effects of engineered nanometals, it is important to determine which species are sensitive to adverse effects of various nanomaterials. In the present study, zebrafish, daphnids, and an algal species were used as models of various trophic levels and feeding strategies. To understand whether observed effects are caused by dissolution, particles were characterized before testing, and particle concentration and dissolution were determined during exposures. Organisms were exposed to silver, copper, aluminum, nickel, and cobalt as both nanoparticles and soluble salts as well as to titanium dioxide nanoparticles. Our results indicate that nanosilver and nanocopper cause toxicity in all organisms tested, with 48-h median lethal concentrations as low as 40 and 60 microg/L, respectively, in Daphnia pulex adults, whereas titanium dioxide did not cause toxicity in any of the tests. Susceptibility to nanometal toxicity differed among species, with filter-feeding invertebrates being markedly more susceptible to nanometal exposure compared with larger organisms (i.e., zebrafish). The role of dissolution in observed toxicity also varied, being minor for silver and copper but, apparently, accounting for most of the toxicity with nickel. Nanoparticulate forms of metals were less toxic than soluble forms based on mass added, but other dose metrics should be developed to accurately assess concentration-response relationships for nanoparticle exposures.
A photoinduced method for converting large quantities of silver nanospheres into triangular nanoprisms is reported. The photo-process
has been characterized by time-dependent ultraviolet-visible spectroscopy and transmission electron microscopy, allowing for
the observation of several key intermediates in and characteristics of the conversion process. This light-driven process results
in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles. Theoretical
calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and for the first
identification of two distinct quadrupole plasmon resonances for a nanoparticle. Unlike the spherical particles they are derived
from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing
multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape.
Early indicators for nanoparticle-derived adverse health effects should provide a relative measure for cytotoxicity of nanomaterials in comparison to existing toxicological data. We have therefore evaluated a human mesothelioma and a rodent fibroblast cell line for in vitro cytotoxicity tests using seven industrially important nanoparticles. Their response in terms of metabolic activity and cell proliferation of cultures exposed to 0-30 ppm nanoparticles (microg g(-1)) was compared to the effects of nontoxic amorphous silica and toxic crocidolite asbestos. Solubility was found to strongly influence the cytotoxic response. The results further revealed a nanoparticle-specific cytotoxic mechanism for uncoated iron oxide and partial detoxification or recovery after treatment with zirconia, ceria, or titania. While in vitro experiments may never replace in vivo studies, the relatively simple cytotoxic tests provide a readily available pre-screening method.
A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH(4) reduction of AgNO(3) in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O(2)/Cl(-) etching of the Ag nanospheres and the reduction of the released Ag(+) by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag(0) atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).
This paper introduces a special issue on the ecotoxicology and environmental chemistry of nanoparticles (NPs), and nanomaterials (NMs), in the journal Ecotoxicology. There are many types of NMs and the scientific community is making observations on NP ecotoxicity to inform the wider debate about the risks and benefits of these materials. Natural NPs have existed in the environment since the beginning of Earth's history, and natural sources can be found in volcanic dust, most natural waters, soils and sediments. Natural NPs are generated by a wide variety of geological and biological processes, and while there is evidence that some natural NPs can be toxic, organisms have also evolved in an environment containing natural NPs. There are concerns that natural nano-scale process could be influenced by the presence of pollution. Manufactured NPs show some complex colloid and aggregation chemistry, which is likely to be affected by particle shape, size, surface area and surface charge, as well as the adsorption properties of the material. Abiotic factors such as pH, ionic strength, water hardness and the presence of organic matter will alter aggregation chemistry; and are expected to influence toxicity. The physico-chemistry is essential to understanding of the fate and behaviour of NPs in the environment, as well as uptake and distribution within organisms, and the interactions of NPs with other pollutants. Data on biological effects show that NPs can be toxic to bacteria, algae, invertebrates and fish species, as well as mammals. However, much of the ecotoxicological data is limited to species used in regulatory testing and freshwater organism. Data on bacteria, terrestrial species, marine species and higher plants is particularly lacking. Detailed investigations of absorption, distribution, metabolism and excretion (ADME) remain to be performed on species from the major phyla, although there are some data on fish. The environmental risk assessment of NMs could be performed using the existing tiered approach and regulatory framework, but with modifications to methodology including chemical characterisation of the materials being used. There are many challenges ahead, and controversies (e.g., reference substances for ecotoxicology), but knowledge transfer from mammalian toxicology, colloid chemistry, as well as material and geological sciences, will enable ecotoxicology studies to move forward in this new multi-disciplinary field.
Manufacturers of clothing articles employ nanosilver (n-Ag) as an antimicrobial agent, but the environmental impacts of n-Ag release from commercial products are unknown. The quantity and form of the nanomaterials released from consumer products should be determined to assess the environmental risks of nanotechnology. This paper investigates silver released from commercial clothing (socks) into water, and its fate in wastewater treatment plants (WWTPs). Six types of socks contained up to a maximum of 1360 microg-Ag/g-sock and leached as much as 650 microg of silver in 500 mL of distilled water. Microscopy conducted on sock material and wash water revealed the presence of silver particles from 10 to 500 nm in diameter. Physical separation and ion selective electrode (ISE) analyses suggest that both colloidal and ionic silver leach from the socks. Variable leaching rates among sock types suggests that the sock manufacturing process may control the release of silver. The adsorption of the leached silver to WWTP biomass was used to develop a model which predicts that a typical wastewater treatment facility could treat a high concentration of influent silver. However, the high silver concentration may limitthe disposal of the biosolids as agricultural fertilizer.
The aim of this study was to use a life-cycle perspective to model the quantities of engineered nanoparticles released into the environment. Three types of nanoparticles were studied: nano silver (nano-Ag), nano TiO2 (nano-TiO2), and carbon nanotubes (CNT). The quantification was based on a substance flow analysis from products to air, soil, and water in Switzerland. The following parameters were used as model inputs: estimated worldwide production volume, allocation of the production volume to product categories, particle release from products, and flow coefficients within the environmental compartments. The predicted environmental concentrations (PEC) were then compared to the predicted no effect concentrations (PNEC) derived from the literature to estimate a possible risk. The expected concentrations of the three nanoparticles in the different environmental compartments vary widely, caused by the different life cycles of the nanoparticle-containing products. The PEC values for nano-TiO2 in water are 0.7--16 microg/L and close to or higher than the PNEC value for nano-TiO2 (< 1 microg/L). The risk quotients (PEC/PNEC) for CNT and nano-Ag were much smaller than one, therefore comprising no reason to expect adverse effects from those particles. The results of this study make it possible for the first time to carry out a quantitative risk assessment of nanoparticles in the environment and suggest further detailed studies of nano-TiO2.
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