Chitosan-mediated synthesis of carbon nanotube-gold nanohybrids

Metal-nanotube nanohybrids were produced by in situ synthesis and stabilization of gold nanoparticles on chitosan-functionalized carbon nanotubes. The formation of gold nanoparticles from tetrachloroauric acid was observed after only a few minutes of contact with the functionalized nanotubes, at room temperature. These results suggest that adsorption of chitosan at the surface of carbon nanotubes permits smooth reduction of the metallic salt and efficient anchoring of gold nanoparticles to the nanotubes.

     

Electrochemical synthesis of gold nanoparticles on the surface of multi-walled carbon nanotubes with glassy carbon electrode and their application

Gold nanoparticles on the surface of multi-walled carbon nanotubes with glassy carbon electrode were prepared using electrochemical synthesis method. The thin films of gold Nanoparticles/multi-walled carbon nanotubes were characterized by scanning electron microscopy, powder X-ray diffraction, and cyclic voltammetry. Electrochemical behavior of adrenaline hydrochloride at gold nanoparticles/multi-walled carbon nanotube modified glassy carbon electrode was investigated. A simple, sensitive, and inexpensive method for determination of adrenaline hydrochloride was proposed.     

High-density assembly of gold nanoparticles on multiwalled carbon nanotubes using 1-pyrenemethylamine as interlinker

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.     

金纳米粒子/碳纳米管复合修饰玻碳电极对对苯二酚氧化还原反应的电催化性能

以对苯二酚为目标化合物比较研究了金纳米粒子、碳纳米管、金纳米粒子/碳纳米管3种纳米粒子修饰电极的电催化性能,结果发现:3种纳米粒子修饰电极均对对苯二酚的电化学信号具有增强作用。电化学阻抗谱和修饰层数试验表明:金纳米粒子的增强效果来自于金纳米粒子的电催化作用,碳纳米管的增强作用来自于电催化作用与大的电极表面积,金纳米粒子/碳纳米管复合修饰电极综合利用了两种纳米粒子的特性,表现出了更为优良的电催化行为。对苯二酚在修饰电极上的电化学过程均为扩散控制过程。     

Controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes

A facile method for controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes is demonstrated. Nitric acid based oxidation was carried out to create carboxylic groups exclusively at the ends of carbon nanotubes, whereas oxidation using a mixture of nitric and sulfuric acid with varied reaction time was carried out to control the population of carboxylic groups on the side walls of nanotubes. In turn, 4-aminothiophenol modified gold nanoparticles were covalently interfaced to these carboxylated multi-walled carbon nanotubes in the presence of a zero length cross-linker, 1-ethylene-3-(3-dimethylaminopropyl) carbodiimide. Raman spectroscopic results showed increase in height of disorder band with each of these successive steps, indicating the increase in degree of functionalization of the carbon nanotubes. Fourier transformed infrared spectroscopic analysis affirmed the functionalization of nanostructures and the formation of nanohybrid. Transmission electron and field emission scanning electron microscopic analysis ascertained the attachment of gold nanoparticles to the ends and side walls of the multi-walled carbon nanotubes. The new hybrid nanostructures may find applications in electronic, optoelectronic, and sensing devices.     

Noncovalent functionalization of multiwalled carbon nanotubes: application in hybrid nanostructures

We developed a reproducible, noncovalent strategy to functionalize multiwalled carbon nanotubes (MWNTs) via embedding nanotubes in polysiloxane shells. (3-Aminopropyl)triethoxysilane molecules adsorbed to the nanotube surfaces via hydrophobic interactions are polymerized simply by acid catalysis and form a thin polysiloxane layer. On the basis of the embedded MWNTs, negatively charged gold nanoparticles are anchored to the nanotube surfaces via electrostatic interactions between the protonated amino groups and the gold nanoparticles. Furthermore, these gold nanoparticles can further grow and magnify along the nanotubes through heating in HAuCl4 aqueous solution at 100 degrees C; as a result these nanoparticles are joined to form continuous gold nanowires with MWNTs acting as templates.     

Effect of gold nanoparticles on an aerosil surface on the fluorescence and Raman spectra of adsorbed tryptophan

We discuss the fluorescence and Raman spectra of the amino acid tryptophan (Trp) in the presence of gold nanoparticles in solution and on the surface of highly dispersed silica (aerosil) containing gold nanoparticles (Au-SiO₂). The fluorescence of Trp is efficiently quenched in the presence of gold nanoparticles both in solution and on the SiO₂ surface. The fluorescence and excitation spectra contain bands for molecular Trp and a charge transfer complex between Trp and the nanoparticles. In the Raman spectra of Trp with gold nanoparticles, considerably enhanced intense vibrations appear for the carboxyl and amino groups and also for the benzene and pyrrole rings. The effect of gold nanoparticles on the Raman spectra of Trp in a heterogeneous system is considerably weakened due to strong light scattering by the dispersed silica.     

Gold nanoparticles for microfluidics-based biosensing of PCR products by hybridization-induced fluorescence quenching

Colloidal gold nanoparticles were used to develop a simple microfluidics-based bioassay that is able to recognize and detect specific DNA sequences via conformational change-induced fluorescence quenching. In this method, a self-assembled monolayer of gold nanoparticles was fabricated on the channel wall of a microfluidic chip, and DNA probes were bonded to the monolayer via thiol groups at one end and a fluorophore dye was attached to the other end of the probe. The created construct is spontaneously assembled into a constrained arch-like conformation on the particle surface and, under which, the fluorescence of fluorophores is quenched by gold nanoparticles. Hybridization of target DNAs results in a conformational change of the construct and then restores the fluorescence, which serves as a sensing method for the target genes. The nanocomposite constructed on the glass surface was characterized by UV absorbance measurement and the quenching efficiency for different fluorophores was evaluated by Stern-Volmer studies. The applicability of proposed assay was first demonstrated by the use of a pair of synthesized complementary and noncomplementary DNA sequences. The method was further applied for the detection of the PCR product of dengue virus with the use of enterovirus as the negative control, and results indicate that the assay is specific for the target gene. Moreover, using this approach, dehybridization, hybridization, and detection of the target genes can be performed in situ on the same microfluidic channel. Thus, this method could be regarded as one-pot reaction and it holds great promises for clinical diagnostics.     

Preparation of Amino-functionalized Multiwall Carbon Nanotube/Gold Nanoparticle Composites

Multiwall carbon nanotubes (MWNT) were modified orderly with carboxyl groups and amino groups. The MWNT/gold nanoparticle composites were formed when the amino‐functionalized MWNT was interacted with gold colloids. The functionalized MWNT was characterized using Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The amino‐functionalized MWNT allows further attaching gold nanoparticles through electrostatic interaction between the negatively charged gold nanoparticles and amino groups on the surface of the MWNT. The composite of gold nanoprticles and amino‐functionalized MWNT was characterized by transmission electron microscopy. This method decorating carbon nanotubes can be used to identify the location of functional groups, i.e. defect sites on carbon nanotubes.     

Synthesis and Fluorescence Properties of Gold Nanoparticles Modified with Dithiocarbamate Functionalized Carbazole

Gold nanoparticles protected by the self-assembled monolayers of 9-[6-(N,N-dibutyl-amino-dithiocarbamate)-hexyl]-carbazole, CHBDTC in short, were prepared via a phase-transfer method. These surface-modified nanoparticles were characterized with UV-vis, photoluminescence spectroscopy and TEM. It was found that the CHBDTC-capped gold nanoparticles were stable under ambient conditions, which is attributed to the protection of the CHBDTC densely packed on the gold nanoparticle surface. The fluorescence emission spectra indicated that the fluorescence of CHBDTC was quenched to some extent by gold nanoparticles. And the CHBDTC-capped Au nanoparticles could be promisingly applied as biomolecular labels and in fabrication of novel photo-based nanodevices as well, owing to the photoactive sensitivity of CHBDTC.     

An experimental and theoretical study of the self-assembly of gold nanoparticles at the surface of functionalized multiwalled carbon nanotubes

This paper reports the findings of a detailed study of the self-assembly of gold nanoparticles at the surface of carbon nanotubes (CNTs). The study included the development of a predictive model for the interactions (charge transfer, van der Waals, osmotic, elastic, nonelastic, and covalent) between tetraoctylammonium bromide-stabilized (TOAB) gold nanoparticles and alkyl- and alkylthiol-modified multiwalled carbon nanotubes (MWCNTs). It also included the measurement of the coverage of gold nanoparticles at the surface of the above MWCNTs as a function of increasing alkyl chain length. One key finding is that it is possible to predict with a high degree of accuracy using the above model the measured coverage of gold nanoparticles adsorbed, either noncovalently or covalently, at the surface of a MWCNT. Another key finding is that, as predicted, under well-defined conditions the measured coverage of nanoparticles is very sensitive to the nature of the modified CNT surface and the contiguous environment, providing valuable insights that will underpin the rational design of functional nanoscale devices assembled from nanoparticle and CNT building blocks.     

Photoinduced electron transfer between chlorophyll a and gold nanoparticles

Excited-state interactions between chlorophyll a (Chla) and gold nanoparticles have been studied. The emission intensity of Chla is quenched by gold nanoparticles. The dominant process for this quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles, although because of a small overlap between fluorescence of Chla and absorption of gold nanoparticles, the energy-transfer process cannot be ruled out. Photoinduced electron-transfer mechanism is supported by the electrochemical modulation of fluorescence of Chla. In absence of an applied bias, Chla cast on gold film, as a result of electron transfer, exhibits a very weak fluorescence. However, upon negatively charging the gold nanocore by external bias, an increase in fluorescence intensity is observed. The negatively charged gold nanoparticles create a barrier and suppress the electron-transfer process from excited Chla to gold nanoparticles, resulting in an increase in radiative process. Nanosecond laser flash experiments of Chla in the presence of gold nanoparticles and fullerene (C60) have demonstrated that Au nanoparticles, besides accepting electrons, can also mediate or shuttle electrons to another acceptor. Taking advantage of these properties of gold nanoparticles, a photoelectrochemical cell based on Chla and gold nanoparticles is constructed. A superior performance of this cell compared to that without the gold film is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode, leading to an enhancement in charge separation efficiency.     

碳纳米管/ZnO纳米复合体的制备和表征

通过将不同直径的ZnO纳米颗粒与碳纳米管连接制备了碳纳米管/ZnO纳米复合体. 将团聚的ZnO纳米颗粒分散并用表面活性剂CTAB使纳米颗粒带正电. 化学氧化碳纳米管使其带负电. ZnO/CTAB微团通过碳管表面羧基与CTAB的静电作用与碳纳米管连接形成纳米复合体. 研究了复合体形成的不同实验条件, 表征了碳纳米管/ZnO纳米复合体的结构并研究了纳米复合体的光学特性. 研究表明, 与碳纳米管连接的ZnO纳米颗粒是互不连接的并保持量子点的特性. 光致发光研究表明ZnO纳米颗粒的激发在纳米复合体中有淬灭.     

A Novel Photo‐Induced Electrochemical Biosensing Method Based on Fluorescent Labeled Molecular Beacon

A novel photo‐induced electrochemical biosensing method has been developed based on fluorescence quenching effect and electrochemical method. In this sensing strategy, the molecular beacon probes labeled with methylene blue were immobilized on the gold nanoparticles modified gold electrode surface firstly; then dopamine was assembled on the electrode surface through electrostatic interaction with gold nanoparticles. Under the continuous illumination, the fluorescence of the methylene blue was quenched by the gold nanoparticles before hybridization; after hybridization with the complementary DNA, methylene blue was far away from the gold nanoparticles and the fluorescence recovered, and then singlet oxygen was generated in the photosensitive reaction of methylene blue in the presence of dissolved oxygen. Singlet oxygen reacted with dopamine, which resulted in the reduction of concentration of the dopamine on the electrode surface. The current of the dopamine on the electrode was used for the sensing of the conformational change of molecular beacon and hence for the detection of target DNA.     

Carbon Nanotube and Gold‐Based Materials: A Symbiosis

Carbon nanotubes constitute a novel class of nanomaterials with potential applications in many areas. The attachment of metal nanoparticles to carbon nanotubes is new way to obtain novel hybrid materials with interesting properties for various applications such as catalysts and gas sensors as well as electronic and magnetic devices. Their unique properties such as excellent electronic properties, a good chemical stability, and a large surface area make carbon nanotubes very useful as a support for gold nanoparticles in many potential applications, ranging from advanced catalytic systems through very sensitive electrochemical sensors and biosensors to highly efficient fuel cells. Here we give an overview on the recent progress in this area by exploring the various synthesis approaches and types of assemblies, in which nanotubes can be decorated with gold nanoparticles and explore the diverse applications of the resulting composites.     

Fluorescence quenching method for the determination of catechol with gold nanoparticles and tyrosinase hybrid system

<正>The determination method of catechol by fluorescence quenching was developed.The assay was based on the combination of the unique property of gold nanoparticles with tyrosinase enzymatic reaction.In the presence of tyrosinase,the fluorescence of gold nanoparticles was quenched by catechol which can be employed to detect catechol.Under the optimal conditions,a linear range 5.0×10~(-7)-1.0×10~(-3) mol L~(-1) and a detection limit 1.0×10~(-7) mol L~(-1) of catechol were obtained.o-Quinone intermediate produced from the enzymatic catalyzed oxidation of catechol was considered to play the main role in the fluorescence quenching.     

甲醛电化学传感器多孔气体扩散电极不同催化层结构与响应性能研究

多孔气体扩散电极的制备是制备甲醛电化学传感器的关键所在, 其中催化层的结构直接影响到传感器的响应性能. 通过柠檬酸三钠还原法合成了纳米金-活性炭、纳米金-碳纳米管催化剂, 制备了甲醛电化学传感器多孔气体扩散电极, 并对电极进行SEM(扫描电子显微镜)物理表征. 在甲醛气体浓度为0.24和0.63 mg/m³时, 电极C具有较好的响应, 在0.1到0.84 mg/m³浓度范围内, 线性方程为y＝10.515x＋4.4049 (R²＝0.9917), 响应时间约80 s. 分析了不同催化剂的气体扩散电极结构与甲醛响应性的关系, 为研制开发性能优良的甲醛电化学传感器奠定了基础.     

Quasi-continuous growth of ultralong carbon nanotube arrays

We report the growth of ultralong (>10 cm) multi-walled and single-walled carbon nanotubes such that the length is limited by the size of the furnace rather than by the termination of growth. The disturbance of microscale laminar flows results in disordered or shorter growth of carbon nanotubes. By downsizing reaction pipes, reaction gas flows are stabilized with low Reynolds numbers. In this way, the catalyst nanoparticles at the end of growing carbon nanotubes can travel a longer distance to grow ultralong nanotubes.     

In situ assembly of gold nanoparticles on nitrogen-doped carbon nanotubes for sensitive immunosensing of microcystin-LR

A simple and green method was developed for in situ assembly of gold nanoparticles on nitrogen-doped carbon nanotubes, and the resulting Au/nitrogen-doped carbon nanotubes nanocomposite was used as an immobilization scaffold of antibody for sensitive immunosensing of microcystin-LR.     

Adsorption characteristics of thionine on gold nanoparticles

Adsorption characteristics of thionine on gold nanoparticles have been studied by using UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), cyclic voltammetry and Fourier transform infrared spectroscopy. With the increasing concentration of gold nanoparticles, the absorption peak intensity of H-type dimers of thionine increases continuously, whereas that of monomers of thionine first increases and then decreases. The addition of gold nanoparticles makes the equilibrium between the monomer and H-type dimer forms of thionine move toward the dimer forms. Furthermore, the adsorption behavior of thionine on gold nanoparticles is also influenced by temperature. TEM images show that the addition of thionine results in an obvious aggregation, and further support the absorption spectral results. The fluorescence intensity of adsorbed thionine is quenched by gold nanoparticles due to the electronic interaction between thionine molecules and gold nanoparticles. Cyclic voltammetric and infrared spectroscopic studies show that the nitrogen atoms of both of the NH2 moieties of thionine strongly bind to the gold nanoparticle surfaces through the electrostatic interaction of thionine with gold nanoparticles. For 15-20 nm particles, the number of adsorbed thionine molecules per gold nanoparticle is about 7.66 x 10(4). Thionine molecules can not only bind to a particle to form a compact monolayer via both of the NH2 moieties, but they can also bind to two particles via their two NH(2) moieties, respectively.