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Single Wall Carbon Nanotube (SWCNT)-Gold Nanorod (AuNR) Conjugates via Thermally-Mild Reaction Conditions
Abstract
An efficient method for the covalent binding of single wall carbon nanotubes (SWCNT) to gold nanorods (AuNR), based on an inverse-electron-demand Diels-Alder (IEDDA) reaction, is established and discussed. This thermally-mild preparation method allows the potential introduction of thermally-labile species to Au-CNT conjugates. This IEDDA approach provides controllable, clean, and facile access to polymer-free organic-soluble AuNR-SWCNT conjugates for potential applications in catalysis, sensing, and electronic devices.
... One important issue that limits the clinical use of CNTs in comparison with GNRs is their nanotoxicity or environmental effects [144]. Fabricating hybrid structures based on GNRs and CNTs could be an intriguing and novel delivery platform in future gene delivery systems [145]. ...
Over the past few decades, gold nanomaterials have shown great promise in the field of nanotechnology, especially in medical and biological applications. They have become the most used nanomaterials in those fields due to their several advantageous. However, rod-shaped gold nanoparticles, or gold nanorods (GNRs), have some more unique physical, optical, and chemical properties, making them proper candidates for biomedical applications including drug/gene delivery, photothermal/photodynamic therapy, and theranostics. Most of their therapeutic applications are based on their ability for tunable heat generation upon exposure to near-infrared (NIR) radiation, which is helpful in both NIR-responsive cargo delivery and photothermal/photodynamic therapies. In this review, a comprehensive insight into the properties, synthesis methods and toxicity of gold nanorods are overviewed first. For the main body of the review, the therapeutic applications of GNRs are provided in four main sections: (i) drug delivery, (ii) gene delivery, (iii) photothermal/photodynamic therapy, and (iv) theranostics applications. Finally, the challenges and future perspectives of their therapeutic application are discussed.
... 521 In the second type of assembly nanostructures, Au NRs are assembled on nanomaterials with large exposed surfaces such as graphene oxide 522−527 and carbon nanotubes. 528 Many semiconductor materials, usually prepared by magnetron sputtering, electrochemical deposition, vapor deposition, and hydrothermal processing, have large surfaces. 529−532 The most common assembly manner is to have Au NRs randomly distributed on the surface of semiconductor nanomaterials. ...
... Likewise, metals, metal oxides, and polymers were also incorporated into 1D iron oxides to form nanocomposites [141]. Nonmagnetic nanocomposites are formed using the metalemetal [142], metalemetal oxide [143], metalepolymer [144], and sometimes metalecarbon allotropes [145]. These nanocomposites are significant in improving the properties of 1D nanostructures to explore their ability to be used in a variety of applications. ...
Ever since the inception of the industrial revolution, artificial acceleration of swift economic development has contributed to the continuous and ever-increasing demand for energy. Fuel consumption, especially conventional fossil fuels, is increasing continuously to meet the energy demand as a consequence. This has two consequences on living things—such as consumption of oxygen and emission of carbon dioxide (CO2) that causes global warming. Two approaches, namely active and passive, are being considered and implemented by different countries to decrease their CO2 emission. The passive approach involves in encouraging energy conservation and refining efficiency of the energy, utilization of fuels with low carbon, improve the consumption of renewable energy, and adopting a greener approach to increase the forest area, while the active approaches involve capturing carbon and storing them in other forms. Due to improvements in the field of nanotechnology, one-dimensional (1D) nanostructures are highly explored to effectively capture carbon. There are several 1D nanostructures namely nanorods, nanofibers, nanotubes, nanowires, nanocylinders, and nanowhiskers. Each morphology exhibits a unique carbon capturing property which makes them superior to other nanoparticles in reducing carbon emission. This chapter is an overview of various 1D nanostructures that are synthesized using several methods. In addition, information about different 1D nanostructures that are used for carbon capturing application and in maintaining the environmental sustainability via carbon storage, sustainable energy production, and pollution control are also discussed.
... Likewise, metals, metal oxides, and polymers were also incorporated into 1D iron oxides to form nanocomposites [141]. Nonmagnetic nanocomposites are formed using the metalemetal [142], metalemetal oxide [143], metalepolymer [144], and sometimes metalecarbon allotropes [145]. These nanocomposites are significant in improving the properties of 1D nanostructures to explore their ability to be used in a variety of applications. ...
Ever since the inception of the industrial revolution, artificial acceleration of swift economic development has contributed to the continuous and ever-increasing demand for energy. Fuel consumption, especially conventional fossil fuels, is increasing continuously to meet the energy demand as a consequence. This has two consequences on living things—such as consumption of oxygen and emission of carbon dioxide (CO2) that causes global warming. Two approaches, namely active and passive, are being considered and implemented by different countries to decrease their CO2 emission. The passive approach involves in encouraging energy conservation and refining efficiency of the energy, utilization of fuels with low carbon, improve the consumption of renewable energy, and adopting a greener approach to increase the forest area, while the active approaches involve capturing carbon and storing them in other forms. Due to improvements in the field of nanotechnology, one-dimensional (1D) nanostructures are highly explored to effectively capture carbon. There are several 1D nanostructures namely nanorods, nanofibers, nanotubes, nanowires, nanocylinders, and nanowhiskers. Each morphology exhibits a unique carbon capturing property which makes them superior to other nanoparticles in reducing carbon emission. This chapter is an overview of various 1D nanostructures that are synthesized using several methods. In addition, information about different 1D nanostructures that are used for carbon capturing application and in maintaining the environmental sustainability via carbon storage, sustainable energy production, and pollution control are also discussed.
... We recently reported the use of an IEDDAr eactiont om odify single-wall carbon nanotubes and highly ordered pyrolytic graphite (HOPG)s urfacesw ithtetrazine-derivatives and tetrazine-terminated gold nanoparticles (tetrazine-AuNP). [19][20][21] In these examples, the IEDDAreaction was carried out under ambient conditions (room temperature, atmosphere pressure) followed by ar apid retro-Diels-Alder reactiont og enerate the final cycloaddition adducts.H ere, we demonstrate the site-specific covalentm odification of an HOPG surface using microcontactp rinting delivery of IEDDA reagents. Ap atterned PDMS stamp thus "inked" with tetrazine derivatives generates ac ovalently modified HOPG surface (Scheme 1). ...
The chemical modification of an sp2 hybridized carbon surface in a controllable manner is very challenging but also crucial for many applications. An inverse electron demand Diels–Alder (IEDDA) reaction using microcontact printing technique is introduced to spatially control the modification of a highly ordered pyrolytic graphite (HOPG) surface under ambient conditions. The covalent modification was characterized by Raman spectroscopy, XPS, and SECM. Tetrazine derivatives can effectively react with an HOPG surface and with microcontact printing methods resulting in spatially patterned surfaces being produced with micrometer‐scale resolution. Printing on small scale: An inverse electron demand Diels–Alder reaction combined with the microcontact printing technique introduces, under ambient conditions, a spatially resolved chemical patterning to highly ordered pyrolytic graphite (HOPG) surfaces.
A glucose biosensor based on a newly designed and synthesized polymer, poly[(E)-6-methyl-6'-(10-methylanthracen-9-yl)-1,1'-diundecyl-[3,3'-biindolinylidene]-2,2'-dione] (namely PIIDAnth), and single walled carbon nanotubes (SWCNTs) was fabricated via an easy one pot electrode preparation and explored as a glucose electrochemical sensor. The key aim of this paper is to emphasize creation of the new surface design of sensing platforms based on a novel polymer and nanomaterial for glucose detection. With the insertion of single walled carbon nanotubes (SWCNTs) into the biosensing system the sensor showed remarkable advantages for glucose detection including high sensitivity and low detection limit. In addition, electrochemical analysis of the polymer was investigated. The enzyme biosensor showed a linear range from 0.05 mM to 1.0 mM (R2 = 0.994) with a great sensitivity of 61.23 µA mM−1cm−2 and low detection limit of 0.026 mM (S/N = 3). The apparent Michaelis-Menten constant (KMapp) was estimated to be 0.8 mM. Cyclic voltammetry (CV) and scanning electron microscopy (SEM) images revealed the electrochemical and morphologic features. The fabricated sensor was also tested in commercial beverages, successfully. Amperometric measurements proved that PIIDAnth/SWCNT/GOx coating is an excellent structure for glucose sensing.
We report a new type of carbon nanotube ring (CNTR) coated with gold nanoparticles (CNTR@AuNPs) using CNTR as a template and surface attached redox-active polymer as a reducing agent. This nanostructure of CNTR bundle embedded in the gap of closely attached AuNPs can play multiple roles as a Raman probe to detect cancer cells and a photoacoustic (PA) contrast agent for imaging-guided cancer therapy. The CNTR@AuNP exhibits substantially higher Raman and optical signals than CNTR coated with a complete Au shell (CNTR@AuNS) and straight CNT@AuNP. The extinction intensity of CNTR@AuNP is about 120-fold higher than that of CNTR at 808 nm, and the surface-enhanced Raman scattering (SERS) signal of CNTR@AuNP is about 110 times stronger than that of CNTR, presumably due to the combined effects of enhanced coupling between the embedded CNTR and the plasmon mode of the closely attached AuNPs, and the strong electromagnetic field in the cavity of the AuNP shell originated from the intercoupling of AuNPs. The greatly enhanced PA signal and photothermal conversion property of CNTR@AuNP were successfully employed for imaging and imaging-guided cancer therapy in two tumor xenograft models. Experimental observations were further supported by numerical simulations and perturbation theory analysis.
A novel amperometric glucose biosensor was fabricated by layer-by-layer self-assembly of gold nanorods (AuNRs) and glucose oxidase (GOD) onto single-walled carbon nanotubes (SWCNTs)-functionalized three-dimensional sol-gel matrix. A thiolated aqueous silica sol containing SWCNTs was first assembled on the surface of a cleaned Au electrode, and then the alternate self-assembly of AuNRs and GOD were repeated to assemble multilayer films of AuNRs-GOD onto SWCNTs-functionalized silica gel for optimizing the biosensor. Among the resulting glucose biosensors, the four layers of AuNRs-GOD-modified electrode showed the best performance. The sol-SWCNTs-(AuNRs- GOD)4/Au biosensor exhibited a good linear range of 0.01–8 mM glucose, high sensitivity of 1.08 μA/mM, and fast amperometric response within 4 s. The good performance of the proposed glucose biosensor could be mainly attributed to the advantages of the three-dimensional sol-gel matrix and stereo self-assembly films, and the natural features of one-dimensional nanostructure SWCNTs and AuNRs. This study may provide a new facile way to fabricate the enzyme-based biosensor with high performance.
The risk-benefit balance for carbon nanotubes (CNTs) dictates their clinical fate. To take a step forward in this crossroad it is compulsory to modulate the CNT in vivo biocompatibility and biodegradability via e. g. chemical functionalization. CNT membranes were functionalised combining a Diels-Alder cycloaddition reaction to generate cyclohexene (-C6H10) followed by a mild oxidisation to yield carboxylic acid groups (-COOH). In vitro proliferation and osteogenic differentiation of human osteoblastic cells were maximized on functionalized CNT membranes (p,f-CNTs). The in vivo subcutaneously implanted materials showed higher biological reactivity, thus inducing a slighter intense inflammatory response relatively to non-functionalized CNT membranes (p-CNTs), but still showing a reduced cytotoxicity profile. Moreover, the in vivo biodegradation of CNTs was superior for p,f-CNTs membranes, likely mediated by oxidation-induced myeloperoxidase (MPO) in neutrophils and macrophages inflammatory milieus. This put evidences for the biodegradability faculty of functionalized CNTs, which potentially avoids long-term tissue accumulation and triggering of acute toxicity. On the whole, the proposed Diels-Alder functionalization was accounted for the improved CNT biological response as referred to biocompatibility and biodegradability profiles. Therefore, CNTs can be considered to be used in bone tissue engineering without noteworthy toxicological threats.
Gold nanoparticles were deposited on carbon nanotubes to provide access to a nanohybrid structure which was involved in the aerobic oxidation of alcohols. The nanohybrid-catalyzed reaction was shown to be highly efficient under mild conditions (i.e. room temperature, air) and selective oxidation of alcohols to the corresponding acids or aldehydes could be achieved, depending on the reaction conditions.
Through various modifications of carbon nanotubes (CNTs), gold nanoparticles were selectively attached to the nanotube and the locations of functional groups were further confirmed. Using cationic polyethyleneamine or anionic citric acid as the dispersant, the surface properties of CNTs could be changed to yield a basic or acidic surface. By electrostatic interaction, the CNTs could be successfully coated with about 10 nm gold nanoparticles. After heat treatment in NH3, about 1–2 nm gold nanocluster-filled nanotubes were achieved. This shows that the heat treatment with NH3 could make CNTs open-ended and generate functional basic groups on the inner wall of the nanotubes.
Carbon nanotubes have shown promise as contrast agents for photoacoustic and photothermal imaging of tumours and infections because they offer high resolution and allow deep tissue imaging. However, in vivo applications have been limited by the relatively low absorption displayed by nanotubes at near-infrared wavelengths and concerns over toxicity. Here, we show that gold-plated carbon nanotubes-termed golden carbon nanotubes-can be used as photoacoustic and photothermal contrast agents with enhanced near-infrared contrast ( approximately 10(2)-fold) for targeting lymphatic vessels in mice using extremely low laser fluence levels of a few mJ cm(-2). Antibody-conjugated golden carbon nanotubes were used to map the lymphatic endothelial receptor, and preliminary in vitro viability tests show golden carbon nanotubes have minimal toxicity. This new nanomaterial could be an effective alternative to existing nanoparticles and fluorescent labels for non-invasive targeted imaging of molecular structures in vivo.
Towards a robust and universal functionalization procedure with alkanethiols for gold nanorods and plasmonic nanoparticles, a straightforward two-step approach is described.
The first Diels-Alder cycloaddition of o-quinodimethane to SWNT has been performed under microwave irradiation.
Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein, we report an efficient method for the covalent functionalization of carbon nanotubes (CNTs) and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide, followed by the addition of diaryliodonium salts. CNTs, including single-walled, double walled, and multi-walled variants (SWCNTs, DWCNTs, and MWCNTs, respectively), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts, relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials.
Gold nanorods have garnered a great deal of scientific interest due to their unique optical properties and have the potential to greatly impact many areas of science and technology. Understanding the structure and chemical makeup of their surfaces, as well as how to tailor them, is of paramount importance in the development of their successful applications. This Feature Article reviews the current understanding of the surface chemistry of as-synthesized gold nanorods, methods of tailoring the surface chemistry of gold nanorods with various inorganic and organic coatings / ligands, and the techniques employed to characterized ligands on the surface of gold nanorods as well as the associated measurement challenges. Specifically, we address the challenges of determining how thick the ligand shell is, how many ligands per nanorod are present on the surface, and where are the ligands located in regiospecific and mixed ligand systems. We conclude with an outlook on the development of the surface chemistry of gold nanorods leading to the development of a synthetic nanoparticle surface chemistry toolbox analogous to that of synthetic organic chemistry and natural product synthesis.
Pyrolysis of chitosan films containing Au(3+) renders 1.1.1 oriented Au nanoplatelets (20 nm lateral size, 3-4 nm height) on a few layers of N-doped graphene (${\overline {{\rm{Au}}} }$/fl-G), while the lateral sides were 0.0.1 oriented. Comparison of the catalytic activity of ${\overline {{\rm{Au}}} }$/fl-G films with powders of unoriented Au NPs supported on graphene showed that ${\overline {{\rm{Au}}} }$/fl-G films exhibit six orders of magnitude enhancement for three gold-catalyzed reactions, namely, Ullmann-like homocoupling, CN cross coupling, and the oxidative coupling of benzene to benzoic acid. This enhancement is the result of the defined morphology, facet orientation of Au nanocrystals, and strong gold-graphene interaction.
We report a simple and easy formation of hybrids between multi-wall carbon nanotubes and gold nanor-ods by one-pot in situ photochemical synthesis. Measurements of surface-enhanced Raman scattering (SERS) through the effect ''coffee ring'' in visible and near infrared (NIR) show high sensitivity with detection of nanomolar concentrations of aromatic dyes. The formation of nanocomposites between carbon nanotubes and gold nanorods without chemical binders simplifies the preparation. Photochemical synthesis is an advance over the techniques previously published.
Oil-contaminated wastewater threatens our environment and health, especially those stabilized by surfactants. Conventional separation protocols become invalid for those surfactants-stabilized nanoemulsions due to their nanometer-sized droplets and extremely high stability. In this paper, photothermal responsive ultrathin Au nanorods / poly(N-isopropylacryamide-co-acrylamide) co-hybrid single-walled carbon nanotubes (SWCNT) nanoporous membranes are constructed. Such membranes are capable of separating oil-in-water nanoemulsions with a maximum flux up to 35890 m2·h-1·bar-1, since they feature hydrophilicity, underwater oleophobicity and nanometer pore sizes. It is remarkable that the permeation flux can be simply modulated by light illumination during the process of separation, due to the incorporation of thermal responsive copolymers and Au nanorods. Meanwhile, it shows ultrahigh separation efficiency (> 99.99 %), desired antifouling and recyclability properties. We anticipate that our ultrathin photothermo-responsive SWCNT-based membranes evoke a potential in the generation of point-of-use water treatment devices.
We report the chemoselective hydrogenation of 4-nitrobenaldehyde to 4-nitrobenzyl alcohol using the unsupported Au spherical nanoparticle and nanorod catalysts at 80 °C in water. A ∼100% selectivity for the 4-nitrobenzyl alcohol product was obtained when the hydrogenation reaction was catalyzed by the unsupported gold catalysts. The Au nanorod catalysts exhibited an aspect-ratio dependent reactivity and generally performed much better than the Au spherical nanoparticle catalyst. The Au nanorod catalysts showed excellent recyclability in the chemoselective hydrogenation (>99% conversion and 100% selectivity after 5 cycles).
Derived from nitrogen-doped carbon nanotubes, the unique stacked cup-shaped hollow compartments, termed as nitrogen-doped carbon nanotube cups (NCNCs), have promising potential as nanoscale containers. In this work, individual NCNCs are effectively isolated out from their as-synthesized stacked structure by a combination of acid oxidation and probe-tip sonication. Based on the intrinsic localized nitrogen functionalities, we managed to effectively cork the NCNCs with gold nanoparticles (GNPs) grown in situ by sodium citrate reduction of chloroauric acid, which formed a graphitic nanocapsule confined with GNP "stoppers". Mechanistically, the growth of the GNP corks starts from the nucleation and welding of gold seeds on the open rims of NCNCs enriched with nitrogen functional groups. Quantitatively, this mechanism is in good agreement with density functional theory (DFT) calculations. A potent oxidizing enzyme of neutrophils, myeloperoxidase, effectively opened the corked NCNCs though GNP detachment, with subsequent complete enzymatic degradation of the graphitic shells. This controlled opening and degradation was further carried out in vitro with human neutrophils, which alludes to new strategies in drug delivery applications based on GNPs-corked NCNCs.
Plasmonic gold nanorod instability and reshaping behavior below melting points are important for many future applications but are yet to be fully understood, with existing nanoparticle melting theories unable to explain the observations. Here, we have systematically studied the photothermal reshaping behavior of gold nanorods irradiated with femtosecond laser pulses to report that the instability is driven by curvature-induced surface diffusion rather than a threshold melting process, and that the stability dramatically decreases with increasing aspect ratio. We successfully utilized the surface diffusion model to explain the observations and found that the activation energy for surface diffusion was dependent on the aspect ratio of the rods, from 0.6 eV for aspect ratio of 5 to 1.5 eV for aspect ratio less than 3. This result indicates that the surface atoms are much easier to diffuse around in larger aspect ratio rods than in shorter rods and can induce reshaping at any given temperature. Current plasmonics and nanorod applications with the sharp geometric features used for greater field enhancement will therefore need to consider surface diffusion driven shape change even at low temperatures.
Chemical derivatization of an sp2 hybridized carbon surface under ambient conditions is a challenge. Tetrazine-linked compounds are shown to react with an sp2 carbon hybridized 2D surface (HOPG) under ambient conditions, via an inverse electron demand Diels-Alder reaction. Taking advantage of the facile derivatization of dichlorotetrazine with thiol- or hydroxyl-containing molecules, a variety of tetrazine-terminated functional molecules can be prepared and applied to the preparation of functional carbon materials. The methodology described here is the mildest approach reported up to date for the derivatization of an sp2 hybridized carbon surface.
Through chemical functionalization of single-walled carbon nanotubes, the prerequisites for possible applications of such nanostructures are established. The derivatized tubes differ from the crude materials in their good solubility, which enables both a more extensive characterization and subsequent chemical reactivity. Current derivatization methods include defect and covalent sidewall functionalization, as well as noncovalent exo- and endohedral functionalization. In this way, for example, a range of nanotubes can be prepared: with sidewall substituents, wrapped with polymers, or with guest molecules included. The current state of the literature is presented in this Minireview.
The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble-metal Pt-based ORR electrocatalysts by nonprecious-metal catalysts is crucial for the large-scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well-defined, bio-inspired ORR catalyst that consists of a biomimetic model compound-an axial imidazole-coordinated porphyrin-covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio-inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state-of-the-art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel-cell technology.
A versatile methodology for the modification of single walled carbon nanotubes (SWCNTs) through an inverse electron demand Diels-Alder reaction with tetrazine-AuNPs (-AuNPs) under ambient conditions is described. A robust covalently bonded hybrid nanocomposite is formed.
We find that citrate-stabilized gold nanoparticles aggregate and precipitate in saline solutions below the NaCl concentration of many bodily fluids and blood plasma. Our experiments indicate that this is due to complexation of the citrate anions with Na(+) cations in solution. A dramatically enhanced colloidal stability is achieved when bovine serum albumin is adsorbed to the gold nanoparticle surface, completely preventing nanoparticle aggregation under harsh environmental conditions where the NaCl concentration is well beyond the isotonic point. Furthermore, we explore the mechanism of the formation of this albumin 'corona' and find that monolayer protein adsorption is most likely ruled by hydrophobic interactions. As for many nanotechnology-based biomedical and environmental applications, particle aggregation and sedimentation are undesirable and could substantially increase the risk of toxicological side-effects, the formation of the BSA corona presented here provides a low-cost bio-compatible strategy for nanoparticle stabilization and transport in highly ionic environments.
Visible light sensing devices using single-walled carbon nanotube (SWNT) film and gold nanoparticles or nanorods were reported. In the devices, half of the SWNT film was decorated with gold nanoparticles or nanorods. When visible light is incident on the device, a temperature difference can be built up between the SWNT film with and without gold nanoparticles (nanorods) due to surface plasmon resonance. As a result, an open circuit voltage can be obtained. The Voc induced and responsivities of these devices are closely related to the wavelength and the intensity of the incident light, indicating the application in visible light detecting.
We present a simple, generally applicable procedure for the assembly of nanoparticles on carbon nanotubes in aqueous solution. The method makes use of polyelectrolytes for wrapping carbon nanotubes and providing them with adsorption sites for electrostatically driven nanoparticle deposition. The method is exemplified by the assembly of gold nanoparticles which results in single, optically labelled carbon nanotubes.
Functionalization of multi-walled carbon nanotubes (MWCNTs) is performed through Diels–Alder (DA) reaction, using either furfuryl alcohol (a diene) or N-(4-hydroxyphenyl)maleimide (NHMI, a dienophile) as a functionalization agent. The structures of the functionalized MWCNTs are characterized with Fourier-transform infrared spectroscopy and Raman spectroscopy. Thermogravimetric analysis results also demonstrate the presence of organic portions of the functionalized MWCNTs. The DA reaction is further applied to incorporate polymer chains onto MWCNT surfaces, using a polyamide with maleimide pendent groups. Transmission electron microscopy images show the presence of a polymer layer of about 2–5nm around the polymer modified MWCNTs.
Many industrial catalysts involve nanoscale metal particles (typically 1–100 nm), and understanding their behavior at the molecular level is a major goal in heterogeneous catalyst research. However, conventional nanocatalysts have a nonuniform particle size distribution, while catalytic activity of nanoparticles is size dependent. This makes it difficult to relate the observed catalytic performance, which represents the average of all particle sizes, to the structure and intrinsic properties of individual catalyst particles. To overcome this obstacle, catalysts with well-defined particle size are highly desirable.
Multi-walled carbon nanotubes (MWNTs) have been reacted with 3,6-diaminotetrazine under heating. This process involves series of interactions between tetrazines and carbon nanotubes including π–π interactions, cycloaddition (Diels–Alder) and cross-linking reactions. These interactions resulted in coating of the MWNTs and in the formation of Y-junctions between nanotubes. Long heating (48 h) of MWNTs with the terazine resulted in a partial destruction of nanotubes due to their excessive functionalisation. The new nanocomposites have been studied by TEM, FTIR and Raman spectroscopy.
Despite the extraordinary promise of single-wall carbon nanotubes, their realistic application in materials and devices has been hindered by processing and manipulation difficulties. Now that this unique material is readily available in near kilogram quantities (albeit still at high cost), research into means of chemical alteration is in full swing. The covalent attachment of appropriate moieties is anticipated to facilitate applications development by improving solubility and ease of dispersion, and providing for chemical attachment to surfaces and polymer matrices. While it is clear that more investigation is needed to elucidate the nature and locality of covalently attached moieties, developments to date indicate that carbon nanotubes may indeed be considered a true segment of organic chemistry. In this contribution, we review the current state of carbon nanotube covalent chemistry, and convey our anxious expectation that further developments will follow.
This review addresses recent advances in carbon-nanotubes (CNT) based electrochemical biosensors. The unique chemical and physical properties of CNT have paved the way to new and improved sensing devices, in general, and electrochemical biosensors, in particular. CNT-based electrochemical transducers offer substantial improvements in the performance of amperometric enzyme electrodes, immunosensors and nucleic-acid sensing devices. The greatly enhanced electrochemical reactivity of hydrogen peroxide and NADH at CNT-modified electrodes makes these nanomaterials extremely attractive for numerous oxidase-and dehydrogenase-based amperometric biosensors. Aligned CNT "forests" can act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centers of enzymes. Bioaffinity devices utilizing enzyme tags can greatly benefit from the enhanced response of the biocatalytic-reaction product at the CNT transducer and from CNT amplification platforms carrying multiple tags. Common designs of CNT-based biosensors are discussed, along with practical examples of such devices. The successful realization of CNT-based biosensors requires proper control of their chemical and physical properties, as well as their functionalization and surface immobilization.
Gold nanorods have received much attention due to their unique optical and electronic properties which are dependent on their shape, size, and aspect ratio. This article covers in detail the synthesis, functionalization, self-assembly, and sensing applications of gold nanorods. The synthesis of three major types of rods is discussed: single-crystalline and pentahedrally-twinned rods, which are synthesized by wet chemistry methods, and polycrystalline rods, which are synthesized by templated deposition. Functionalization of these rods is usually necessary for their applications, but can often be problematic due to their surfactant coating. Thus, general strategies are provided for the covalent and noncovalent functionalization of gold nanorods. The review will then examine the significant progress that has been made in controllable assembly of nanorods into various arrangements. This assembly can have a large effect on measurable properties of rods, making it particularly applicable towards sensing of a variety of analytes. Other types of sensing not dependent on nanorod assembly, such as refractive-index based sensing, are also discussed.
Single-walled carbon nanotubes (SWNTs) with various unique optical properties are interesting nanoprobes widely explored in biomedical imaging and phototherapies. Herein, DNA-functionalized SWNTs are modified with noble metal (Ag or Au) nanoparticles via an in situ solution phase synthesis method comprised of seed attachment, seeded growth, and surface modification with polyethylene glycol (PEG), yielding SWNT-Ag-PEG and SWNT-Au-PEG nanocomposites stable in physiological environments. With gold or silver nanoparticles decorated on the surface, the SWNT-metal nanocomposites gain an excellent concentration and excitation-source dependent surface-enhanced Raman scattering (SERS) effect. Using a near-infrared (NIR) laser as the excitation source, targeted Raman imaging of cancer cells labeled with folic acid (FA) conjugated SWNT-Au nanocomposite (SWNT-Au-PEG-FA) is realized, with images acquired in significantly shortened periods of time as compared to that of using nonenhanced SWNT Raman probes. Owing to the strong surface plasmon resonance absorption contributed by the gold shell, the SWNTs-Au-PEG-FA nanocomposite also offers remarkably improved photothermal cancer cell killing efficacy. This work presents a facile approach to synthesize water-soluble noble metal coated SWNTs with a strong SERS effect suitable for labeling and fast Raman spectroscopic imaging of biological samples, which has been rarely realized before. The SWNT-Au-PEG nanocomposite developed here may thus be an interesting optical theranostic probe for cancer imaging and therapy.
Multi-walled carbon nanotube (MWCNT)/thionine/gold nanoparticle composites were prepared by binding gold nanoparticles to the surfaces of thionine-coated carbon nanotubes. TEM images show gold nanoparticles distributed uniformly on nanotube walls and ends. UV–Vis, Raman, FT-IR, and zeta potential measurements were used to examine the properties of the resulting products. The composites demonstrate significant electrocatalytic activity for oxygen reduction. Although only gold nanoparticles were investigated here, the method could be easily extended to attach other metallic nanoparticles to the sidewalls of carbon nanotubes.
Recent developments in nanostructure self-assembly from gold and silver particles are reviewed. A brief historical background of the field is given, followed by a selection of topics which are of particular current interest. An overview of the preparation of thiol-stabilised gold and silver nanoparticles and their spontaneous self-organisation into well-ordered superlattices is presented. Distance-dependent metal insulator transitions in ensembles of nanoparticles are discussed, along with a previously unpublished measurement of optical properties of dithiol-linked thin films of gold nanoparticles. Recent approaches to more complex nano-architectures are reviewed, including the use of various templates and of DNA base pair recognition. Some aspects of nanoscopic surface chemistry of gold particles including the evolution of molecular recognition sites are reviewed. Current and potential future applications are discussed.
A simple method has been developed to directly attach gold nanoparticles (Au-NPs) on carbon nanotubes (CNTs) with high dispersivity by using a small amount of ethanol to reduce the interfacial tension between CNTs and aqueous solution and impart solubility for CNTs in the solution containing Au-NPs. Both SEM and TEM characterization showed that Au-NPs distributed uniformly on the walls of CNTs. UV–vis spectra of the solution before and after attachment revealed that Au-NPs in the original solution were completely loaded on the CNTs without loss of Au source. The content of Au-NPs on CNTs could be controlled readily by adjusting the weight ratio between Au particles and CNTs. The electrochemical catalytic properties of the so-produced composites were characterized, and the samples showed a catalytic activity for the oxygen reduction reaction that is higher than those reported in the literature.
The zero-band-gap electronic structure of graphene enables it to function as either the diene or the dienophile in the Diels-Alder reaction, and this versatile synthetic method offers a powerful strategy for the reversible modification of the electronic properties of graphene under very mild conditions.
The unique morphology and structure of carbon nanotubes (CNT) keep attracting a great number of researchers to explore the novel properties of these materials. Among various surface functionalization techniques, oxidation of CNTs is probably the most widely studied. Early treatment techniques involved gas-phase oxidation in air and oxidative plasmas. Carboxylated CNTs were extensively used as precursors for further covalent modification of CNTs, through esterification and/or amidation reactions. Moreover, a few other direct esterification/amidation procedures of oxidized CNTs were reported. In one of them, acid purified SWCNTs were treated with molten urea, which functions both as solvent and as reactant. Modification of CNTs with ionic liquids is expected to improve their compatibility and stability, enhancing the potential of CNTs in applications such as sensors and actuators, by improving the electrical contact with media.
The synthesis of precisely defined nanoscale hybrid materials remains a challenge at the frontier of chemistry and material science. In particular, the assembly of diverse high-aspect ratio one-dimensional materials such as gold nanorods and carbon nanotubes into functional systems is of ever increasing interest due to their electronic and sensing applications. To meet these challenges, methods for interfacing gold nanorods with carbon materials such as single-walled carbon nanotubes (SWCNTs) in a regio-controlled manner are needed. Herein, we report a method for the regiospecific synthesis of terminally linked gold nanorod-SWCNTs based on a nanotube surface protection strategy. The key to our approach is a SWCNT surface protection procedure allowing for selective functionalization of the SWCNT termini.
Described is a bioorthogonal reaction that proceeds with unusually fast reaction rates without need for catalysis: the cycloaddition of s-tetrazine and trans-cyclooctene derivatives. The reactions tolerate a broad range of functionality and proceed in high yield in organic solvents, water, cell media, or cell lysate. The rate of the ligation between trans-cyclooctene and 3,6-di-(2-pyridyl)-s-tetrazine is very rapid (k2 2000 M-1 s-1). This fast reactivity enables protein modification at low concentration.
Customizable ligand exchange of gold nanorods (NRs) is described. NRs are synthesized with the cationic surfactant cetyltrimethylammonium bromide (CTAB) which is exchanged with thiolated ligands that enable suspension in buffer. Exchange is achieved by a two phase extraction. First, CTAB is removed from the NR-CTAB by extracting the NRs into an organic phase via the ligand dodecanethiol (DDT). The NR-DDT are then extracted into an aqueous phase by mercaptocarboxylic acids (MCA), HS-(CH 2)n -COOH (n = 5, 10, and 15). Ligands can be further customized to thiolated poly(ethylene glycol), PEG MW (MW = 356, 5000, and 1000). Ligand-exchanged NRs (NR-MCA and NR-PEG(MW)) are stable in buffer, do not aggregate, and do not change size upon ligand exchange. They can be run in agarose gel electrophoresis with narrow bands, indicating uniform charge distribution and enabling quantitative analysis. DNA functionalization of NR-MCA is straightforward and quantifiable, with minimal nonspecific adsorption.
[structure: see text] The viability of the Diels-Alder (DA) cycloaddition of conjugated dienes onto the sidewalls of single-wall carbon nanotubes is assessed by means of a two-layered ONIOM(B3LYP/6-31G:AM1) approach. Whereas the DA reaction of 1,3-butadiene on the sidewall of an armchair (5,5) nanotube is found to be unfavorable, the cycloaddition of quinodimethane is predicted to be viable due to the aromaticity stabilization at the corresponding transition states and products.
Short gold nanorods of average lengths ranging between 20 and 100 nm (with corresponding aspect ratios of 2 and 4) were synthesized in excellent yield (approximately 97%). These nanorods were characterized by dark-field microscopy, UV-visible spectrophotometry, and transmission electron microscopy. Temporal evolution of rod shape had also been followed by UV-visible spectrophotometry and transmission electron microscopy and indicates that the nanorods briefly increase in length, then increase slightly in width, as they grow. The effect of the synthetic parameters on the rod dimension and yield was explored to find out suitable conditions to produce short nanorods; short nanorods have both plasmon bands in the visible region of the spectrum, which is a valuable property for sensor applications.
Poly(aminobenzene sulfonic acid) (PABS) and polyethylene glycol (PEG) were covalently attached to single-walled carbon nanotubes (SWNTs) to form water-soluble graft copolymers. Quantitative near-IR (NIR) spectroscopic studies of these SWNT graft copolymers indicate a water solubility of about 5 mg/mL, and atomic force microscopy studies show a fairly uniform length and diameter. On the basis of thermogravimetric analysis, the loading of SWNTs in the graft copolymers is estimated to be 30% for SWNT-PABS and 71% for SWNT-PEG. NIR spectroscopic studies of SWNT-PABS show that this graft copolymer has a ground state that is a hybrid of the electronic structures of the isolated PABS and SWNT macromolecules.
(Graph Presented) With strings attached: Gold nanorods undergo uniform electrostatic assembly on multiwall carbon nanotubes (MWNTs) to form strings of rods with end-to-end contacts (see picture, PSS = polystyrene sulfonate, PDDA = poly(diallyldimethyl)-ammonium chloride). This arrangement results in uniaxial plasmon coupling, and the polarization-dependent optical response has been used to monitor the degree of alignment of carbon nanotubes within polymer films.
This contribution describes the synthesis of gold nanorod (Au NR)/single-wall carbon nanotube (SWCNT) heterojunctions assembled directly on Si/SiOx substrates. SWCNTs are attached to amine-functionalized Si/SiOx substrates, and Au monolayer-protected clusters (MPCs) are adsorbed to the surface of SWCNTs through hydrophobic interactions. Seed-mediated reduction of HAuCl4 with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB) onto the Au MPCs leads to the growth of larger Au nanostructures directly on the SWCNTs. Au NRs account for 19% of the nanostructures, some of which are attached directly to the sidewall and some at the ends of the SWCNTs. Raman spectroscopic measurements of SWCNTs before and after growth of the Au nanostructures reveal that the presence of Au leads to an approximately 50-fold enhancement of the Raman scattering signal. Combining 1D nanostructures of different materials (Au and carbon in this example) is of fundamental interest and may find use in nanoelectronics, chemical sensing, electrochemical, and spectroscopy applications.
The preparation of nanocomposite materials from carbon nanotubes (CNTs) and metal or metal oxide nanoparticles has important implications to the development of advanced catalytic and sensory materials. This paper reports findings of an investigation of the preparation of nanoparticle-coated carbon nanotube composite materials. Our approach involves molecularly mediated assembly of monolayer-capped nanoparticles on multiwalled CNTs via a combination of hydrophobic and hydrogen-bonding interactions between the capping/mediating shell and the CNT surface. The advantage of this route is that it does not require tedious surface modification of CNTs. We have demonstrated its simplicity and effectiveness for assembling alkanethiolate-capped gold nanoparticles of 2-5 nm core sizes onto CNTs with controllable coverage and spatially isolated character. The loading and distribution of the nanoparticles on CNTs depend on the relative concentrations of gold nanoparticles, CNTs, and mediating or linking agents. The composite nanomaterials can be dispersed in organic solvent, and the capping/linking shells can be removed by thermal treatment to produce controllable nanocrystals on the CNT surfaces. The nanocomposite materials are characterized using transmission electron microscopy and Fourier transform infrared spectroscopy techniques. The results will be discussed in terms of developing advanced catalytic and sensory nanomaterials.
In this article, we describe the formation of carbon nanotube (CNT)-gold nanoparticle composites in aqueous solution using 1-pyrenemethylamine (Py-CH2NH2) as the interlinker. The alkylamine substituent of 1-pyrenemethylamine binds to a gold nanoparticle, while the pyrene chromophore is noncovalently attached to the sidewall of a carbon nanotube via pi-pi stacking interaction. Using this strategy, gold nanoparticles with diameters of 2-4 nm can be densely assembled on the sidewalls of multiwalled carbon nanotubes. The formation of functionalized gold nanoparticles and CNT-Au nanoparticle composites was followed by UV-vis absorption and luminescence spectroscopy. After functionalization of gold nanoparticles with 1-pyrenemethylamine, the distinct absorption vibronic structure of the pyrene chromophore was greatly perturbed and its absorbance value was decreased. There was also a corresponding red shift of the surface plasmon resonance (SPR) absorption band of the gold nanoparticles after surface modification from 508 to 556 nm due to interparticle plasmon coupling. Further reduction of the pyrene chromophore absorbance was observed upon formation of the CNT-Au nanoparticle composites. The photoluminescence of 1-pyrenemethylamine was largely quenched after attaching to gold nanoparticles; formation of the CNT-Au nanoparticle composites further lowered its emission intensity. The pyrene fluoroprobe also sensed a relatively nonpolar environment after its attachment to the nanotube surface. The present approach to forming high-density deposition of gold nanoparticles on the surface of multiwalled carbon nanotubes can be extended to other molecules with similar structures such as N-(1-naphthyl)ethylenediamine and phenethylamine, demonstrating the generality of this strategy for making CNT-Au nanostructure composites.
Within the different classes of tubes made of organic or inorganic materials and exhibiting interesting electronic, mechanical, and structural properties, carbon nanotubes (CNTs) are exremely promising for applications in materials science and medicinal chemistry. However, the lack of solubility and the difficult manipulation in any solvents have imposed great limitations to the use of CNT. To address these limitations, several approaches for modifying these quasi one-dimensional structures have been developed and these fall into three categories: (a) the covalent attachment of chemical groups through reactions onto the π-conjugated skeleton of CNT; (b) the noncovalent adsorption or wrapping of various functional molecules; and (c) the endohedral filling of their inner empty cavity. With these approaches, laboratories expect to have full control of size and shape, thus developing new applications in composites and electronics.
Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.
We describe herein the synthesis of functional gold nanorods suitable for carrying out "click" chemistry reactions. Gold nanorods modified with a copolymer containing sulfonate and maleic acid groups have been conjugated to a bifunctional azide molecule (amine-PEG-azide). The maleic acid molecules in the copolymer participate in carbodiimide-mediated amide bond formation with amine groups of the azide linker, whereas the sulfonate groups prevent nanorod aggregation in water. Spectroscopic and zeta-potential measurements have been used to confirm the successful surface modification of the gold nanorods. These azide-functionalized nanorods can carry out chemical reactions based on click chemistry. As a case study, we have demonstrated the "clicking" of azide-nanorods to an acetylene-functionalized enzyme, trypsin, by a copper-catalyzed 1,3-dipolar cycloaddition reaction. The enzyme is not only stable after bioconjugation but is also biologically active, as demonstrated by its digestion of the protein casein. For comparison, the biological activity of trypsin conjugated to gold nanorods by two other commonly used methods (carbodiimide-mediated covalent attachment via amide bond formation and simple electrostatic adsorption) has been studied. The enzyme conjugated by click chemistry demonstrates improved biological activity compared with other forms of bioconjugation. This general and simple approach is easy, specific with higher yields, environmentally benign, and applicable to a wide range of analytes and biomolecules.