Optical and Electrochemical Combination Sensor with Poly‐Aniline Film Modified Gold Surface and Its Application for Dissolved Oxygen Detection

Poly‐aniline (PAn) film can be oxidized by contacting oxygen in an electron‐transfer reaction and its redox state, for instance the open circuit potential and the dielectric constant, is quantitatively related to oxygen concentration. This feature may contribute to an improved application of dissolved oxygen (DO) detection with the combined optical and electrochemical sensor. In this paper, PAn is used as a sensing surface to detect DO by the combination sensor composed of electrochemistry and total internal reflection imaging ellipsometry (EC‐TIRIE). Results demonstrate that both optical and electrical signals show a logarithmic correlation with DO concentration (0–20 ppm). Compared with the results obtained only with the gold surface, both the optical and electrical signals of the EC‐TIRIE sensor for DO detection are amplified with the PAn modified gold surface.     

Nanoelectrode ensembles based on conductive polyaniline/poly(acrylic acid) using porous sol–gel films as template

Porous sol–gel (PSG) film has been utilized as a template for the electrochemical polymerization of aniline in presence of poly(acrylic acid) (PAA). The presence of electroactive polyaniline (PAn)/PAA within the porous skeleton of the sol–gel films has been confirmed using cyclic voltammetry, UV–vis spectrometry and atomic force microscopic measurements. The densities and the sizes of the nanoelectrodes can be controlled easily using electrochemical methods. The conductive polymer “wires” of PAn/PAA formation in PSG matrix can behave as an ensemble of closely-spaced but isolated nanoelectrodes. Moreover, the nanoelectrode ensembles based on conductive PAn/PAA for glucose biosensing are fabricated by immobilization of glucose oxidase (GOx) and Nafion onto the surface of conductive polymer. Owing to the biocompatibility of PSG and electro-activity of PAn/PAA at neutral pH regions, the glucose biosensor shows excellent characteristics and performance, such as low detection limit and fast response time.     

Template‐free synthesis of polyaniline nanobelts as a catalytic counter electrode in dye‐sensitized solar cells

Polyaniline (PAn) nanobelts were synthesized by simply mixing aniline and hydrochloric acid aqueous solution with ammonium peroxydisulfate and hydrochloric acid aqueous solution at room temperature without any templates. The PAn nanobelt paste with polytetrafluoroethylene as binder is proper for low‐cost and efficient casting processes such as doctor blade method, screen printing, spin‐casting, and even roll‐to‐roll painting. The porous network structure of the PAn nanobelt counter electrode was obtained after drying the paste on the conductive glass. The as‐prepared PAn nanobelt counter electrode showed nearly equivalent electrochemical catalytic activity as that of thermal decomposed Pt counter electrode, owing to the well‐connected conductive network and high active surface area. The power conversion efficiency of dye‐sensitized solar cell with PAn nanobelt counter electrode attained 90% of the value of the cell with Pt counter electrode. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel electrochemical SPR biosensor

In this paper, we demonstrate for the first time that upon electrochemical oxidation/reduction, the transition in the conductivity of polyaniline (PAn) film on gold electrode surface leads to a large change of surface plasmon resonance (SPR) response due to a change in the imaginary part of dielectric constant of PAn film. Based on the amplifying response of SPR to the redox transformation of PAn film as a direct result of the enzymatic reaction between horseradish peroxidase (HRP) and PAn in the presence of H₂O₂, a novel PAn-mediated HRP sensor has been fabricated. The electrochemical SPR biosensor, unlike a usual binding assay with SPR, can afford a larger SPR response, and can also be reused by reducing the PAn film electrochemically to its reduced state. This method opens up a new route to the fabrication of SPR biosensor.     

Reactive coupling of 4-vinylaniline with hydrogen-terminated Si(100) surfaces for electroless metal and "synthetic metal" deposition

Pristine and resist-patterned Si(100) substrates were etched by aqueous HF to produce hydrogen-terminated silicon (H-Si(100)) surfaces. The H-Si(100) surface was then subjected to UV-induced reactive coupling of 4-vinylaniline (VAn) to produce the VAn monolayer-modified silicon (VAn-Si) surface. The VAn-Si surface was first functionalized with a "synthetic metal" by oxidative graft polymerization of aniline with the aniline moieties of the coupled VAn molecules. The composition and topography of the VAn-Si and polyaniline (PAn)-grafted VAn-Si (PAn-VAn-Si) surfaces were characterized by X-ray photoelectron spectroscopy and atomic force microscopy, respectively. The doping-undoping (protonation-deprotonation) and redox-coupling (metal reduction) behavior, as well as the electrical conductivity, of the surface-grafted PAn were found to be similar to those of the aniline homopolymer. The VAn-Si surface was also funtionalized by the electroless plating of copper. Not only did the VAn layer provide chemisorption sites for the palladium catalyst, in the absence of prior sensitization by SnCl2, during the electroless plating process, it also served as an adhesion promotion layer and a low-temperature diffusion barrier for the electrolessly deposited copper. Finally, micropatterning of the grafted PAn and of the electrolessly deposited copper were demonstrated on the resist-patterned VAn-Si surfaces.     

聚苯胺颗粒电极的制备与其电化学行为

采用循环伏安法,以含苯胺(An)的硫酸溶液为电解质,采用循环伏安技术在Pt微盘电极上得到随机、不连续沉积的聚苯胺(PAn)微颗粒和PAn膜.实验结果表明:H2SO4浓度、苯胺浓度、电位扫描上限和扫速对电化学合成随机、不连续沉积的PAn微颗粒具有重要影响.不连续随机沉积的PAn微颗粒电极与PAn膜电极在锂离子(Li-ion)电池电解质溶液中的行为有明显差异,不连续随机沉积的PAn微颗粒电极可以清楚地得到氧化还原电流峰,而PAn膜电极无法形成清晰的氧化还原电流峰.采用较缓慢扫描速度更有利于形成良好"结晶"的不连续PAn颗粒电极,该种电极可以同时具有高比能量和可逆性能.     

FTIR spectroscopic characterization of Nafion®–polyaniline composite films employed for the corrosion control of stainless steel

Nafion?–polyaniline (PAn) composite films deposited by a two-step process on a stainless steel (SS) substrate were characterized in this study using Fourier transform infrared (FTIR) spectroscopy under various conditions employed to evaluate their anticorrosion properties. The SS|Nafion? electrode was first prepared by placing a certain amount of Nafion? on the SS substrate, and then polymerization of aniline was carried out potentiodynamically on the SS|Nafion? electrode. The SS|Nafion?–PAn electrodes subjected to both potentiodynamic polarization and open-circuit conditions in sulfuric acid solutions without and with chlorides appeared to have distinct differences in their FTIR spectra. It is proposed that under the electrochemical conditions used in this study, the PAn is mostly formed inside the Nafion? membrane with a high proportion of oligomers influencing the ionic transport through the membrane. The inhibition of pitting corrosion arises primarily from the enhanced permselectivity of the composite film due to the Nafion? membrane that prevents chloride transport. An essential beneficial effect comes also from the PAn redox properties on the growth of the passive oxide film. Even under severe corrosion conditions, Nafion???/em>PAn films retain their redox activity and chemical stability, whereas the membrane crystallinity seems to be enhanced.     

FTIR spectroscopic characterization of Nafion®–polyaniline composite films employed for the corrosion control of stainless steel

Nafion®–polyaniline (PAn) composite films deposited by a two-step process on a stainless steel (SS) substrate were characterized in this study using Fourier transform infrared (FTIR) spectroscopy under various conditions employed to evaluate their anticorrosion properties. The SS|Nafion® electrode was first prepared by placing a certain amount of Nafion® on the SS substrate, and then polymerization of aniline was carried out potentiodynamically on the SS|Nafion® electrode. The SS|Nafion®–PAn electrodes subjected to both potentiodynamic polarization and open-circuit conditions in sulfuric acid solutions without and with chlorides appeared to have distinct differences in their FTIR spectra. It is proposed that under the electrochemical conditions used in this study, the PAn is mostly formed inside the Nafion® membrane with a high proportion of oligomers influencing the ionic transport through the membrane. The inhibition of pitting corrosion arises primarily from the enhanced permselectivity of the composite film due to the Nafion® membrane that prevents chloride transport. An essential beneficial effect comes also from the PAn redox properties on the growth of the passive oxide film. Even under severe corrosion conditions, Nafion®–PAn films retain their redox activity and chemical stability, whereas the membrane crystallinity seems to be enhanced.

     

基于金纳米颗粒信号放大效应电化学检测DNA聚合酶

基于金纳米颗粒(AuNPs)比表面积大、 尺寸小和能够承载大量DNA片段的特点, 建立了一种免标记、 简便、 快速检测DNA聚合酶Klenow fragment exo-(KF^-)的电化学方法. 首先将巯基化的DNA引物片段修饰在金电极上, 然后加入模板DNA链以及修饰有报告DNA链的金纳米颗粒(AuNPs-DNA), 模板DNA链能同时与DNA引物片段和修饰在AuNPs上的报告DNA链进行互补杂交形成"三明治"结构, 从而将AuNPs-DNA修饰在电极表面; 当加入电活性物质钌铵(RuHex)后, RuHex可通过静电吸附作用结合在DNA上. AuNPs上修饰的报告DNA链能够吸附大量RuHex, 导致电化学信号放大. 当加入脱氧核糖核苷三磷酸(dNTPs)以及KF^-聚合酶后, 引物片段发生延伸反应, 将与模板DNA链杂交的AuNPs-DNA竞争下来, 带走大量的RuHex, 使电信号降低, 从而实现对聚合酶的检测. 实验结果表明, 利用该方法可以检测到5 U/mL的KF^-.     

Enhanced Bioelectrocatalysis Using Single‐Walled Carbon Nanotubes (SWCNTs)/Polyaniline Hybrid Systems in Thin‐Film and Microrod Structures Associated with Electrodes

The charge transport properties in composites consisting of pyrene sulfonic acid‐functionalized single‐walled carbon nanotubes embedded in polyaniline, PAn/SWCNTs, and polystyrene sulfonate‐doped PAn, PAn/PSS, are compared in thin‐film and microrods configurations. The PAn/SWCNTs and PAn/PSS microrods were prepared by the electropolymerization of the respective components in porous alumina membranes coated with a conductive gold support, followed by the dissolution of the membrane template. The charge transport upon the oxidation of the PAn/SWCNTs planar film or microrods structures is ca. 3.5–4.0‐fold faster than upon the oxidation of the PAn/PSS planar film or microrods structures, respectively. The faster charge transport in the PAn/SWCNTs films and microrods is used to enhance the mediated bioelectrocatalyzed oxidation of glucose in the presence of glucose oxidase (GOx). The bioelectrocatalyzed oxidation of glucose in the presence of the PAn/SWCNTs in the planar film and microrods structures is ca. 2‐fold and up to 6‐fold (depending on the potential) enhanced as compared to the respective PAn/PSS configurations.     

Electrochemical Quantitative Analysis of Nucleic Acids Using β‐Cyclodextrin Modified Gold Electrode

We present an electrochemical biosensor for the analysis of nucleic acids upon hybridization on the β‐cyclodextrin (β‐CD)‐modified gold electrode. The strategy is based on the following: The 5’‐ferrocene‐labeled single stranded capture probe DNA (5’‐fc‐ss‐DNA) was incorporated into the cavity of thiolated β‐CD which was immobilized on the surface of gold electrode. After hybridization of complementary target DNA, hybridized double stranded DNA (ds‐DNA) was released from the cavity of β‐CD. The difference of electrochemical properties on the modified gold electrode was characterized by cyclic voltametry and surface plasmon resonance. We successfully applied this method to the investigation of the sensor responses due to hybridization on various concentrations of applied target DNA. As a result, the label‐free electrochemical DNA sensor can detect the target DNA with a detection limit of 1.08 nM. Finally, our method does not require either hybridization indicators or other signalling molecules such as DNA intercalaters which most of electrochemical hybridization detection systems require.     

Preparation of Gold Nanotube by Direct Electrodeposition for Biosensors

A simple method to fabricate gold nanotube by means of a direct electrodeposition is constructed, utilizing anodic aluminum oxide (AAO) as a template. The performances of gold nanoelectrode have been characterized with cyclic voltammetric technique and scanning electron microscope (SEM). The SEM image of as-prepared gold nanoelectrode shows that the surface of electrode was covered with honeycomb gold tube with average pore diameter 200 nm. Its cyclic voltammetric shows the peak current is 6.25 times larger than the bare Au electrode, so the new honeycomb gold nanoelectrode was obviously better than conventional gold electrode. Microperoxidase-11 (MP-11) was immobilized on the electrode and characterized with cyclic voltammetric technique. It was demonstrated that the gold nanotube not only could offer a friendly environment to immobilize MP-11, but also enhance the electron transfer ability between protein molecules and the underlying electrodes.     

原位紫外-可见光谱和电化学方法研究苯胺聚合过程中的降解

用电化学及光谱电化学研究了硫酸溶液中苯胺在玻碳电极上的聚合降解过程 ,在 - 0 2～ 1 0V电位范围 ,循环伏安图显示了四对氧化还原峰 .通过比较聚苯胺 (PAn)膜在硫酸空白溶液和含对氨基苯酚 (PAP)的硫酸溶液中的循环伏安曲线及电化学聚合时溶液的紫外 可见吸收光谱 ,证明了PAn膜的降解产物PAP的存在 ,同时原位现场紫外 可见吸收光谱法初步研究了苯胺聚合降解的动力学过程 .     

Detection of DNA immobilized on bare gold electrodes and gold nanoparticle-modified electrodes via electrogenerated chemiluminescence using a ruthenium complex as a tag

Electrogenerated chemiluminescence (ECL) for DNA hybridization detection is demonstrated based on DNA that was self-assembled onto a bare gold electrode and onto a gold nanoparticles modified gold electrode. A ruthenium complex served as an ECL tag. Gold nanoparticles were self-assembled on a gold electrode associated with a 1,6-hexanedithiol monolayer. The surface density of single stranded DNA (ssDNA) on the gold nanoparticle modified gold electrode was 4.8?×?10¹⁴ molecules per square centimeter which was 12-fold higher than that on the bare gold electrode. Hybridization was induced by exposure of the target ssDNA gold electrode to the solution of ECL probe consisting of complementary ssDNA tagged with ruthenium complex. The detection limit of target ssDNA on a gold nanoparticle modified gold electrode (6.7?×?10^?12 mol L^?1) is much lower than that on a bare gold electrode (1.2?×?10^?10 mol L^?1). The method has been applied to the detection of the DNA sequence related to cystic fibrosis. This work demonstrates that employment of gold nanoparticles self-assembled on a gold electrode is a promising strategy for the enhancement of the sensitivity of ECL detection of DNA.     

DNA sequencing with titanium nitride electrodes

We construct a hydrogen‐bond based metal–molecule–metal junction, which contains two identical “reader” molecules, one single DNA base as a bridged molecule, and two titanium nitride electrodes. Hydrogen bonds are formed between “reader” molecules and DNA base, whereas titanium–sulfur bonds are formed between “reader” molecules and titanium nitride electrodes. We perform electronic structure calculations for both the bare bridged molecule and the full metal–molecule–metal system. The projected density of states shows that when the molecule is connected to the titanium nitride electrode, the energy levels of the bridged molecule are shifted, with an indirect effect on the hydrogen bonds. This is similar to the case for a gold electrode but with a more pronounced effect. We also calculate the current–voltage characteristics for the molecular junctions containing each DNA base. Results show that titanium nitride as an electrode can generate distinct conductance for each DNA base, providing an alternative electrode for DNA sequencing. © 2013 Wiley Periodicals, Inc.     

Studies on biotin–avidin indirect conjugated technology for a piezoelectric DNA sensor

Because of their high sensitivity, piezoelectric sensor techniques are extremely useful for environmental or clinical analysis. We developed a piezoelectric crystal DNA biosensor for the detection of the hybridization reaction based on the self-assembled monolayer technology and biotin–avidin system. 3,3′-Dithiopropionic acid was applied to form a self-assembled monolayer (SAM) on the gold surface of the quartz crystal. Avidin was coated on the gold electrode conjugated with 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide (EDC) and N-hydroxysuccinimide (NHS), and then biotinylated nucleotide acids were immobilized on the gold electrode surface through the specific interaction of biotin and avidin. Our results indicated that, using this immobilization method, the piezoelectric DNA sensor shows a higher sensitivity and specificity in detecting the hybridization reaction. The sensor can be used repeatedly by electrode regeneration.     

以DNA为模板构造苯胺-DNA复合物纳米线和聚苯胺纳米导线

在溶液中, 以DNA为模板构造出了线性的苯胺-DNA复合物纳米线. 用压缩气流将得到的复合物纳米线拉直并固定到云母基底上. 用原子力显微镜(AFM)可观察到形貌规整的苯胺-DNA复合物纳米线. 苯胺单体在溶液中能从各个方向上组装到DNA分子上, 从而使DNA模板分子的表面包裹了一层苯胺. 以苯胺-DNA复合物纳米线为前驱体通过进一步化学氧化聚合得到了以DNA为模板的聚苯胺纳米导线.     

沉淀聚合制备磺酸掺杂的聚苯胺

以二丁基萘磺酸(DBNSA)或十二烷基苯磺酸(DBSA)为有机酸,水为主要反应介质的条件下进行沉淀聚合直接制备有机酸掺杂的聚苯胺(PAn).讨论了酸度、温度和氧化剂用量等反应条件对产物的影响。2L规模扩大实验的产率约为75%～80%,所得PAn具有高电导率(3.0S·cm^-1),并易溶于普通有机溶剂。其中PAn-DBNSA在各方面较具优势。     

聚苯胺包裹的金纳米粒子的合成和表征及初步应用

用苯胺作还原剂还原氯金酸合成了金纳米结构. TEM实验表明, 苯胺还原氯金酸能生成苯胺齐聚物或其聚合物包裹的金球形纳米粒子. XPS分析表明, 金纳米粒子包覆的聚合物层带正电荷. 该纳米粒子能用于电极表面纳米结构组装及氧化还原性的生物大分子的电化学研究, 实现了超氧化物歧化酶(SOD)在这种带正电荷的金纳米粒子表面的直接电子转移.     

检测痕量Hg~(2+)的DNA电化学生物传感器

通过自组装方法将修饰有二茂铁基团的富T序列DNA分子(DNA-Fc)固定在金电极表面,得到了一种基于DNA修饰电极的电化学汞离子(Hg2+)传感器.当溶液中有Hg2+存在时,Hg2+可与修饰电极上DNA的T碱基发生较强的特异结合,形成T-Hg2+-T发卡结构,使DNA分子构象发生改变,其末端具有电化学活性的二茂铁基团远离电极表面,电化学响应随之发生变化.示差脉冲伏安法(DPV)结果显示:DNA末端二茂铁基团的还原峰在0.26V(vs饱和甘汞电极(SCE))附近,峰电流随溶液中Hg2+浓度的增加而降低;Hg2+浓度范围在0.1nmol·L-1-1μmol·L-1时,电流相对变化率与Hg2+浓度的对数呈现良好的线性关系.该修饰电极对Hg2+的检测限为0.1nmol·L-1,可作为痕量Hg2+检测的电化学生物传感器.干扰实验也表明,该传感器对Hg2+具有良好的特异性与灵敏度.