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Color transition upon nanoparticle aggregation. (a) Experimental results show the change of color (through Hue values) from dispersed (black line) to aggregated (cyan line) for spherical, cubic, and decahedral NPs. (b) Theoretical results show the change of Hue values upon clustering of 10 NPs/cluster with an interparticle gap of (left column) 6 nm and (right column) 2 nm. The circle markers along the lines have the computed colors in RGB space obtained from spectral analysis.
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Spurred by outstanding optical properties, chemical stability, and facile bioconjugation, plasmonic metals have become the first-choice materials for optical signal transducers in biosensing. While the design rules for surface-based plasmonic sensors are well-established and commercialized, there is limited knowledge of the design of sensors based...
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... calculated ( The invariance of color with the increasing size of spherical nanoparticles suggests that this particular shape exhibits high tolerance to size polydispersity, which is quite the opposite behavior for faceted nanoparticles. The increase of electron interactions at more localized spaces in the Dec-NPs broadens the absorption spectrum, 30 leading to a drastic change of the H value, which is more pronounced with increasing size distribution (Figure 4a, bottom panel). Thus, using faceted nanoparticles (e.g., cubes, or decahedra) in colorimetric sensing demands high monodispersity. ...
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... the maximum allowed change of Hue values is 0.45 (1−0.55) for an aggregation-based colorimetric sensor (see the arrow in the Hue wheel, Figure S6). Our experimental data confirmed such a limit (Figure 4a). For the three shapes used, the H value is nearly unity while nanoparticles remain dispersed and progressively decreases toward the limiting value of 0.55 upon aggregation. ...
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... RGB values generated from the extinction spectra confirmed that red-colored dispersed nanoparticles undergo a transition toward blue color with decreasing interparticle distance. At interparticle gap distance of 6 nm and small diameter, the calculated Hue values barely decreased (first purple point in the line of cyan points in Figure 4b), which is the experimental trend found for Sph-NPs, but not for Cub-NPs and Dec-NPs. In contrast, for larger dimensions, the theoretical Hue values decreased toward 0.55, corroborating the experimental trend in all cases. ...
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... contrast, for larger dimensions, the theoretical Hue values decreased toward 0.55, corroborating the experimental trend in all cases. Further decrease of the interparticle gap distance down to 2 nm (keeping constant the number of 10 nanoparticles per cluster) showed an improved agreement of the Hue value between theory and experiments (blue points in Figure 4a,b), suggesting that this shorter distance reproduces more accurately the molecular dimensions in between the aggregated nanoparticles. ...
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... the larger the ΔH, the greater the colorimetric sensitivity. By taking the calculated Hue values from both experimental and theoretical results in Figure 4, we calculated ΔH as a function of the nanoparticle size for the three types of particles (i.e., ΔH Sph , ΔH Cub , and ΔH Dec , respectively, in Figure 5a−c). As expected, the efficiency of colorimetric sensing based on the red-to-blue color transition showed a peak centered at an optimal (maximum) diameter window for each shape, where the values of ΔH are the highest (∼80%). ...
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... 3-fold increase in ΔH was observed while decreasing the gap from 6 to 2 nm (10 NPs/ cluster) for a decahedron of 20 nm. Interestingly, the effect of interparticle distance on the color difference was more Figure 5. (a−c) FOM ΔH (eq 1) resulted from the theoretical and experimental Hue values (see Figure 4) of (a) spherical, (b) cubic, and (c) decahedral nanoparticle clusters (ΔH Sph , ΔH Cub , and ΔH Dec , respectively) of 10NPs/cluster with gap distances of g = 6 nm (theor., black trianglemarked lines), 2 nm (theor., red square-marked lines), and experimental ΔH (gray circle-marked lines). (d−i) Calculated extinction cross sections and RGB colors of (d, g) spherical, (e, h) cubic, and (f, i) decahedral single gold nanoparticles (d−f) and clusters (g−i), for the sizes in which ΔH is maximum for each theoretical case (see the blue circles in (a−c)). ...
Citations
... For example, in colorimetric sensing involving oxidative etching, it becomes crucial to identify the dimensions yielding the most significant change in the LSPR position within the extinction spectrum in the visible range. 26,36,64 On the other hand, when designing thermoplasmonic nanoparticles 65 for applications such as hyperthermia treatment, the focus shifts toward determining the dimensions where absorption gets maximized at the specific wavelength of interest. 15,18 More generally, studying the thermoplasmonic response concerning the geometry and topology of nanoparticles enables the prediction of local temperature gradients and the control of thermal effects in the surrounding medium when particles are illuminated. ...
Unraveling the nuanced interplay between the morphology and the optical properties of plasmonic nanoparticles is crucial for targeted applications. Managing the relationship becomes significantly complex when dealing with anisotropic nanoparticles that defy a simple description using parameters like length, width, or aspect ratio. This complexity requires computationally intensive numerical modeling and advanced imaging techniques. To address these challenges, we propose a detailed structural parameter determination of gold nanoparticles using their two-dimensional projections (e.g., micrographs). Employing gold bipyramids (AuBPs) as a model morphology, we can determine their three-dimensional geometry and extract optical features computationally for comparison with the experimental data. To validate our inversion model’s effectiveness, we apply it to derive the structural parameters of AuBPs undergoing shape modification through oxidative etching. In summary, our findings allow for the precise characterization of structural parameters for plasmonic nanoparticles during shape transitions, potentially enhancing the comprehension of nanocrystal growth and optimizing plasmonic material design for various applications.
... However, there is not much information on how the size and concentration of AuNPs may affect the detection performance. The geometrical parameters allow maximizing of color difference upon nanoparticle aggregation [10]. AuNP size also played an important role in the colorimetric detection of nickel ions (Ni(II)) [11]. ...
It is very important to determine the presence of toxic Cr(VI) in aqueous environment. Detection of Cr(VI) using AuNPs has been carried out based on the oxidation or etching principle, which results in the change of localized surface plasmon resonance. In this work, the effects of size and concentration of colloidal AuNPs on the Cr(VI) sensing characteristics were studied by both simulation and experiment. In the simulation study using MNPBEM toolbox, the etching process was described as shrinking of AuNPs with total volume loss reflecting the concentration of Cr(VI) as oxidizing ions. The experiment was carried out by exposing colloidal AuNPs with different size and concentration to Cr(VI). The AuNPs were obtained from laser-induced photochemical process, in which aqueous solution of Au ions were subjected to femtosecond laser irradiation. The simulation results showed wider blue-shift of λLSPR per total volume loss when larger AuNPs were employed and higher intercept value of extinction decrease per total volume loss when more AuNPs were present in the system. Correspondingly, the experiment demonstrated more distinct color change and wider λLSPR per Cr(VI) concentration when larger AuNPs were used. More concentrated colloid showed still-red color after Cr(VI) etching, representing higher intercept value of extinction decrease per Cr(VI). Both simulation and experiment results show that, in etching-based Cr(VI) sensing, large AuNPs displayed wider LSPR wavelength shift compared to the small nanoparticles. On the other hand, concentration of AuNPs contributes to the intensity change and higher concentration of AuNPs offers higher Cr(VI) sensing range. This result provided an insight on how colorimetric sensor performance might be affected by the choice of nanoparticle size and concentration used in the system.
... One of the most obvious advantages of colorimetric detection is that the results can be observed by the naked eye. In addition, colorimetric detection has a simple operation, high sensitivity, great selectivity, and a low cost [25][26][27][28][29]. Therefore, colorimetric detection can fulfill the requirements for application in POCT. ...
A pipette-free and fully integrated device that can be used to accurately recognize the presence of infectious pathogens is an important and useful tool in point-of-care testing, particularly when aiming to decrease the unpredictable threats posed by disease outbreak. In this study, a paper device is developed to integrate the three main processes required for detecting infectious pathogens, including DNA extraction, loop-mediated isothermal amplification (LAMP), and detection. All key reagents, including sodium dodecyl sulfate (SDS), NaOH, LAMP reagents, and carmoisine, are placed on the paper device. The paper device is operated simply via sliding and folding without using any bulky equipment, and the results can be directly observed by the naked eye. The optimized concentrations of sodium dodecyl sulfate (SDS), sodium hydroxide (NaOH), and carmoisine were found to be 0.1%, 0.1 M, and 0.5 mg/mL, respectively. The paper device was used to detect Enterococcus faecium at concentrations as low as 102 CFU/mL within 60 min. Also, E. faecium spiked in milk was successfully detected using the paper device, demonstrating the feasible application in real sample analysis.
... Aggregation induces changes in the morphology and size of Au NPs, resulting in shifts in their LSPR peaks, as well as changes in visible light color [80,81]. The characteristic absorption peak of LSPR for Au NSPs is at 520 nm and its solution appears bright burgundy. ...
The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.
It is crucial to realize the point‐of‐care (POC) testing of harmful analytes, capable of saving limited agricultural resources, assisting environmental remediation, ensuring food safety, and enabling early disease diagnosis. Compared with other conventional POC sensing strategies, aggregation‐based analytical chemistry facilitates the practical‐oriented development of POC nanosensors by altering the aggregation status of nanoprobes through the action of multiple aggregation‐induced “forces” originating from the targets. Herein, we have proceeded with a comprehensive review focusing on the aggregation‐based analytical chemistry in POC nanosensors, covering aggregation‐induced “forces”, aggregation‐induced signal transductions, aggregation‐induced POC nanosensing strategies, and their applications in biomolecular monitoring, food safety analysis, and environmental monitoring. Finally, challenges existing in practical applications have been further proposed to improve their sensing applications, and we expect our review can speed up the development of cost‐effective, readily deployable, and time‐efficient nanosensors through aggregation‐based analytical chemistry.
Gold nanoparticles (GNPs) are highly promising in cancer therapy, wound healing, drug delivery, biosensing, and biomedical imaging. Furthermore, GNPs have anti-infammatory, anti-angiogenic, antioxidants, anti-proliferative and anti-diabetic efects. The present study presents an eco-friendly approach for GNPs biosynthesis using the cell-free supernatant of Streptomyces albogriseolus as a reducing and stabilizing agent. The biosynthesized GNPs have a maximum absorption peak at 540 nm. The TEM images showed that GNPs ranged in size from 5.42 to 13.34 nm and had a spherical shape. GNPs have a negatively charged surface with a Zeta potential of −24.8 mV. FTIR analysis identifed several functional groups including C–H, –OH, C–N, amines and amide groups. The crystalline structure of GNPs was verifed by X-ray difraction and the well-defned and distinct difraction rings observed by the selected area electron difraction analysis. To optimize the biosynthesis of GNPs using the cell-free supernatant of S. albogriseolus, 30 experimental runs were conducted using central composite design (CCD). The artifcial neural network (ANN) was employed to analyze, validate, and predict GNPs biosynthesis compared to CCD. The maximum experimental yield of GNPs (778.74 μg/mL) was obtained with a cell-free supernatant concentration of 70%, a HAuCl4 concentration of 800 μg/mL, an initial pH of 7, and a 96-h incubation time. The theoretically predicted yields of GNPs by CCD and ANN were 809.89 and 777.32 μg/mL, respectively, which indicates that ANN has stronger prediction potential compared to the CCD. The anticancer activity of GNPs was compared to that of doxorubicin (Dox) in vitro against the HeP-G2 human cancer cell line. The IC50 values of Dox and GNPs-based treatments were 7.26 ± 0.4 and 22.13 ± 1.3 µg/mL, respectively. Interestingly, treatments combining Dox and GNPs together showed an IC50 value of 3.52 ± 0.1 µg/mL, indicating that they targeted cancer
cells more efciently.
