Modification of composites of block copolymers–gold nanoparticles with enzymes and their characterization by electrochemical techniques

In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer–gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.     

静电组装金纳米粒子制备局域表面等离子体共振传感膜

采用聚电解质自组装技术制备局域表面等离子体共振(LSPR)传感膜的方法, 在玻璃基片上依次沉积聚电解质PDDA, PSS和PVTC, 并通过静电吸附构建胶体金纳米粒子自组装膜形成LSPR传感膜. 利用扫描电镜对LSPR传感膜表面形貌以及膜中金纳米粒子的粒径进行了表征, 同时通过紫外-可见消光光谱对其灵敏度和渗透深度等重要参数进行检测. 研究结果表明, 所制备的LSPR传感膜粒子分布均匀、单分散性好、稳定性高、重现性好; 消光峰位对样品溶液折射率的检测灵敏度为71 nm/RIU, 相应的峰强检测灵敏度为0.21 AU/RIU, 对表面吸附层的渗透深度约为16 nm.     

大粒径单分散金纳米粒子的水相合成

近年来,随着纳米科技的兴起,纳米尺度的金颗粒以其独特的光学、电学性质［１-３］在许多领域表现出潜在的应用价值,引起了人们浓厚的研究兴趣［４-７］．迄今为止,已有多种制备金纳米粒子的方法见诸报导．制备简便、单分散性好、粒径可控,一直是各种方法追求的目标．...     

The preparation and characterization of poly(o-phenylenediamine)/gold nanoparticles interface for immunoassay by surface plasmon resonance and electrochemistry

The poly-o-phenylenediamine (PoPD) nonconducting film and gold nanoparticles (AuNPs) were combined to fabricate AuNPs/PoPD film, which is used as a novel biocompatible interface for the immobilization of antibody and develop a simple and sensitive label-free immunoassay for the detection of the related antigen (human immunoglobulin G (IgG)). Surface plasmon resonance (SPR) and electrochemical methods were used to provide the real-time information about the polymer film growth, assembling of various sizes of gold nanoparticles, anti-human IgG antibody (anti-hIgG) immobilization and the antigen–antibody interaction. The microstructures of the PoPD and AuNPs/PoPD films were characterized by atomic force microscopy (AFM). These results demonstrated that AuNPs were uniformly dispersed on the porous surface of PoPD film, which formed a nano-structure biocompatible AuNPs/PoPD interface. The use of gold nanoparticles and PoPD film could enhance the immunoassay sensitivity and anti-nonspecific property of the resulting immunoassay electrode. Additionally, the reproducibility and preliminary application of anti-hIgG/AuNPs/PoPD/Au electrode for SPR detection of hIgG was also evaluated.     

基于网状混合自组装膜的压电免疫传感器及其应用

结合纳米金及混合自组装技术, 制备了一种新型网状混合膜, 提出了一种新的生物分子固定化方法, 研制了一种用于检测人血清抗精子抗体的压电免疫传感器. 首先, 将纳米金溶胶、巯基丙酸和1,6-二巯基己烷按一定的比例混合制得网状混合自组装膜, 然后将此膜组装到压电石英晶振的金电极表面, 经EDC/NHS活化后, 再将抗原固定到电极上, 实现对抗精子抗体的检测. 结果表明, 该方法能明显提高抗体抗原结合效率, 从而提高传感器的灵敏度, 并降低传感界面的非特异性吸附. 将此传感器应用于人血清抗精子抗体的检测, 线性范围为10~800 mU/mL, 检出限为7 mU/mL. 此传感器为抗精子抗体的临床检测提供了新平台.     

A novel capacitive immunosensor based on gold colloid monolayers associated with a sol-gel matrix

A capacitive sensing method based on self-assembling gold nanoparticles to the surface of the sol-gel modified electrode has been developed for the direct detection of the human IgG in human serum. The capacitance of the immunosensor corresponding to the concentration of human IgG is investigated by alternating current impedance. The formed mercaptopropyltriethoxysilane (MPTS) film is ultrathin; the immobilization density of antibodies is high because of high surface-volume area of the assembled gold nanoparticles and the biological macromolecules when immobilized on gold nanoparticles can retain their bioactivity. This capacitive immunosensor prepared with present method can provide high sensitivity. The linear calibration curve was obtained in the range 8.3-2128 ng/ml, with a detection limit of 3.3 ng/ml when plotted versus the logarithm of the antigen concentration. After each immunoassay, the regeneration of the electrode could be performed through washing in basic solution without obvious decrease in response. No cross-reactivity was observed with other protein species. The dependence of sol-gel modified electrode stability on the pH value and ion strength was studied. The insulating properties of the different layers of the immunosensor were also investigated.     

In-situ synthesis of poly(dimethylsiloxane)-gold nanoparticles composite films and its application in microfluidic systems

We presented a simple approach for in-situ synthesis of poly(dimethylsiloxane) (PDMS)-gold nanoparticles composite film based on the special characteristics of PDMS itself. It is an environmentally safe synthesis method without the requirement of additional reducing/stabilizing agents. The region where the resulting gold nanoparticles distribute (in the matrix or on the surface of the polymer) and the size of the nanoparticles, as well as the colour of the free-standing films, can be simply controlled by adjusting the ratio of curing agent and the PDMS monomer. The chemical and optical properties of these composite films were studied. Using such a method, gold nanoparticle micropatterns on PDMS surfaces can be performed. And based on the gold nanoparticles micropattern, further modification with antibodies, antigens, enzymes and other biomolecules can be achieved. To verify this ability, an immobilized glucose oxidase (GOx) reactor in microchannels was built and its performance was studied. The experiments have shown that the resulting composite film may have a lot of potential merits in protein immobilization, immunoassays and other biochemical analysis on PDMS microchips.     

An ionic surfactant-mediated Langmuir-Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering

A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir-Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixture in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge density of AuNPs. Since DTAB binds the gold surface by a coulombic force, rather than a chemical bonding, it is easily replaced by target molecules for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approximately 1.2 × 10(6) using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approximately 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.     

A novel amperometric immunosensor based on three-dimensional sol-gel network and nanoparticle self-assemble technique

A novel hepatitis B surface antigen (HBsAg) immunosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed mercaptopropyltrimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, hepatitis B surface antibody (HBsAb) was adsorbed onto the surface of the gold nanoparticles. Thus, an interfacial design of bare gold electrode (BGE)/MPS/Au/HBsAb was prepared to detect HBsAg in human serum based on the specific reaction of HBsAb and HBsAg. The electrochemistry of ferricyanide redox reaction was used as a marker to probe the interface and as a redox probe to determinate HBsAg. The main conditions of the assembly of MPS sol-gel, gold nanoparticles, the immobilization of HBsAb, and incubation time were investigated in detail. Compared with the glutaraldehyde binding approach, the antibodies immobilized by this method present larger amount and higher immunoactivity. The linearity of HBsAg in the range of 2-360 ng/mL with the correlation coefficient of 0.998 was obtained. This immunosensor system was evaluated on several clinical sample, the analytical results obtained by this method were in agreement with those detected by the enzyme-linked immunosorbent assay (ELISA) method, indicating a promising alternative tool for clinical diagnosis. Moreover, the studied immunosensor exhibited good reproducibility, long-term stability, high sensitivity and specificity.     

Surface-guided self-assembly of silver nanoparticles on edges of heterogeneous surfaces

A general method for the generation of two-dimensional (2D) ordered silver nanoparticles (av 45 nm) ring array has been demonstrated via controllable self-assembly. The selective self-assembly is conducted on the edges of a gold coated polyelectrolyte film. This film is fabricated using the monolayer polystyrene (PS) spheres (av 600 nm) on a substrate as template, followed by depositing a positively charged polyelectrolyte and gold colloids (av 17 nm) via the layer-by-layer (LbL) self-assembly technique, and finally by eliminating the PS monolayer. This gold coated polyelectrolyte film has a regular pattern of sharp edges, and those edges are composed of abundant polyelectrolyte. This heterogeneous surface is easily prepared and universal for site-selective absorption of nanoparticles (silver nanoparticles in this paper, av 45 nm). This surface-guided self-assembly is powerful for fabricating micro/nanostructures on the edges of prepatterns. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the products.     

Gold nanoshells on polystyrene cores for control of surface plasmon resonance

A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.     

Rapid colorimetric sensing of tetracycline antibiotics with in situ growth of gold nanoparticles

A colorimetric assay utilizing the formation of gold nanoparticles was developed to detect tetracycline antibiotics in fluidic samples. Tetracycline antibiotics showed the capability of directly reducing aurate salts into atomic gold which form gold nanoparticles spontaneously under proper conditions. The resulted gold nanoparticles showed characteristic plasmon absorbance at 526 nm, which can be visualized by naked eyes or with a spectrophotometer. UV–vis absorbance of the resulted gold nanoparticles is correlated directly with the concentrations of tetracycline antibiotics in the solution, allowing for quantitative colorimetric detection of tetracycline antibiotics. Reaction conditions, such as pH, temperature, reaction time, and ionic strength were optimized. Sensitivity of the colorimetric assay can be enhanced by the addition of gold nanoparticle seeds, a LOD as low as 20 ng mL⁻¹ can be achieved with the help of seed particles. The colorimetric assay showed minimum interference from ethanol, methanol, urea, glucose, and other antibiotics such as sulfonamides, amino glycosides etc. Validity of the method was also evaluated on urine samples spiked with tetracycline antibiotics. The method provides a broad spectrum detection method for rapid and sensitive detection of reductive substances such as tetracycline antibiotics in liquid and biological samples.     

Adsorption Behaviors of 4-Mercaptobenzoic Acid on Silver and Gold Films

The adsorption behaviors of 4-mercaptobenzoic acid on silver and gold nanoparticles were studied by surface-enhanced Raman scattering (SERS) and density functional theory. The silver and gold films by electrodeposition have the same excellent characteristics as SERS-active substrates. At the same, the SERS spectra indicate that 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of gold nanoparticles through the S atom, and that the carboxyl group is far away from surface of gold nanoparticles, and that there is a certain angle between the plane of benzene ring and gold film. However, 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of silver nanoparticles through the carboxyl group, and the S atom is far away from surface of silver nanoparticles, and there is also a certain angle between the plane of benzene ring and the surface of silver nanoparticles. Here it is demonstrated the calculated Raman frequencies are in good agreement with experimental values, and the calculated Raman frequencies are also helpful to infer the adsorption behaviors of 4-mercaptobenzoic acid molecules.     

Semi-quantitative determination of cationic surfactants in aqueous solutions using gold nanoparticles as reporter probes

Concentrations of cationic surfactants in aqueous solutions have been estimated on the basis of changes in the color of gold nanoparticles, used as reporter probes. We have shown that the colors of gold nanoparticles with anionic protective groups on their surfaces shift from red to indigo/purple and then back to red in a range of cationic surfactant solutions in which concentrations vary from very low to above the theoretical CMCs. The color changes occur near the theoretical CMCs, presumably because the presence of surfactant micelles in the solution prevents the gold nanoparticles from aggregating. We have used gold nanoparticles as reporter probes to determine the concentrations of cationic surfactants in products such as hair conditioners, which often contain large amounts of alkyltrimethylammonium halides. Although this approach can only provide an estimate, it can be performed simply by addition of a given amount of gold nanoparticles to a series of diluted solutions, without the need for instruments or labor-intensive procedures. Figure Photographs of a series of diluted hair conditioner solutions with added gold nanoparticles

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湿化学镀SPR金基底及其性能表征

建立一种由单一水相操作的表面等离子体共振法(SPR)制备金基底.即:在3-氨基丙基三甲氧基硅烷(APTMS)修饰的玻璃片上自组装一层细小的金胶纳米粒子,以此为催化模板,利用化学镀技术在纳米尺度范围内控制金膜的均匀增长,获得优异SPR信号响应所需要的金膜形貌和厚度.紫外光谱(UV-vis),透射电镜(TEM)观测表明,纳米金膜催化模板粒径约为2.5 nm.扫描电镜(SEM)观察湿化学镀SPR金基底均匀分布,粒径约为40 nm.与商品化真空镀金基底相比,湿化学镀金基底对乙醇的SPR响应强度相当,且可调控性更高.     

SERS of C60/C70 on gold-coated filter paper or filter film influenced by the gold thickness

SERS of C(60)/C(70) adsorbed on gold nanoparticles coated on filter paper or filter film was studied. As a new SERS substrate, dried gold-coated filter paper or filter film has a high SERS activity, whose enhancement factor can be up to about 10(5), because it avoided the influence of solvents in C(60)/C(70) solution and water in gold hydrosols. The influence of the gold thickness coated on filter paper or filter film to SERS of C(60)/C(70) adsorbed on gold nanoparticles was mainly discussed. It is indicated that the SERS effect of C(60)/C(70) was very sensitive to the distribution and aggregated characteristics of gold nanoparticles, and the SERS intensity of each mode increased at its own proportion, but it integrally tended to saturation when the thickness of colloidal gold coatings increased.     

Electrochemical growth of two-dimensional gold nanostructures on a thin polypyrrole film modified ITO electrode

Two-dimensional gold nanostructures have been fabricated by electrochemical deposition of gold nanoparticles onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. By controlling the electrodeposition conditions, gold nanoparticles with dendritic rod, sheet, flower-like (consisting of staggered nanosheets), and pinecone-like structures were generated. The flower-like gold nanoparticles showed high catalytic activity on electrochemical reduction of oxygen, and its activity was measured to be approximately 25 times that of gold pinecones and 10(4) times that of gold nanosheets in terms of gold weight. The pinecone-like nanoparticles can form a compact film with nano-/microscale binary structure like a lotus leaf surface. After modification with n-dodecanethiol, the surface showed superhydrophobic properties with a water contact angle of 153.4 degrees and a tilt angle of 4.4 degrees (5 microL droplet).     

A novel cobalt hexacyanoferrate nanocomposite on CNT scaffold by seed medium and application for biosensor

In this paper, for the first time, we introduced the seed-mediated method to the growth of cobalt hexacyanoferrate nanoparticles (CoNPs), using 3.5 nm gold nanoparticles as seeds and multiwalled carbon nanotubes (MWCNTs) as growth scaffold which would both show synergistic action toward the reduction of H₂O₂. Via gold seeds, the one-step fabrication of CoNPs on the glassy carbon electrode is simple without any linking reagents, which will ingeniously exert the electrochemical properties of cobalt hexacyanoferrate. Combined with glucose oxidase, the sensing surface is applied as a biosensor for glucose. The growth of CoNPs is a chemical deposition process around the small Au nanoseed particles. The nanoseeds bridge the CoNPs and CNTs to form a smart nanocomposite. Spherical CoNPs have a relatively moderate dispersion on the three-dimensional network of CNTs with relatively even diameter ca. 100 nm. Whereas, in the control experiments without gold seeds cobalt hexacyanoferrate can only form continuous films, of which the size is far from nanolevel and the catalytic ability is poor. The synthesis and fabrication/modification of CoNPs are simple and fast without prior preparation of CoNPs and lengthy process of cross-linking. The amount of the seeds and CNTs, growth time and concentration of growth solution were investigated. Scanning electron microscopy (SEM) and electrochemical method were used.     

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.     

Selective dissolution of the silver component in colloidal Au and Ag multilayers: a facile way to prepare nanoporous gold film materials

Colloidal Au/Ag multilayer films were prepared by alternate assembly of Au nanoparticles with a size of 5 +/- 1.2 nm and Ag nanoparticles with a size of 10 +/- 2.4 nm by using 1,5-pentanedithiol as cross-linker. Nanoporous gold films with a ligament size of 26.7 +/- 4.6 nm were then prepared by selective dissolution of sacrificial templates of silver particles in colloidal Au/Ag multilayers. The complete dissolution of Ag particles in colloidal Au/Ag multilayers in a mixture solution of 3.0 mM HAuCl(4) and 3 M NaCl took place at room temperature without damage of the colloidal Au film. This method to prepare nanoporous gold films was further extended to the preparation of nanoporous gold nanotubes by depositing colloidal Au/Ag film on the inner wall of anodic aluminum oxides (AAO) followed by dissolution of colloidal Ag and removal of AAO templates.