Electrochemical deposition of polypyrrole/graphene oxide composite on microelectrodes towards tuning the electrochemical properties of neural probes

By exploiting the electrostatic interaction between positively charged pyrrole cation radicals and negatively charged graphene oxide (GO) sheets, we prepared polypyrrole/graphene oxide (PPy/GO) composite films by a one-step electrochemical process. We studied the effects of the polymerization current density and the GO content in electrolyte on the formation of PPy/GO coatings onto platinum neural microelectrode sites. As compared with pure PPy film, PPy/GO coatings show a rougher surface feature with micrometer-scale bulges. The impedance of the PPy/GO coated Pt electrode is only about 10% of the bare Pt electrode at the biological relevant 1 kHz, while the charge capacity density is more than two orders of the magnitude of the bare Pt electrode. Moreover, the PPy/GO coated Pt electrodes show higher performance than the PPy coated electrodes for the application of neural probe.     

Analysis of dc and ac properties of humidity sensor based on polypyrrole materials

Polypyrrole (PPY) materials were prepared by using chemical polymerization at room temperature for 96 h. A resistive-type humidity sensor was fabricated on a ceramic substrate with Ag–Pd interdigital electrodes. The humidity-sensing mechanism of the polypyrrole materials was discussed in terms of capacitance, direct current, complex impedance and dielectric loss properties. The discussion on the sensing mechanism indicated that not only electrons or ions but also dipoles contributed to the conduction in the whole relative humidity range.     

电化学酶联免疫传感器的发展概述

电化学酶联免疫传感器广泛应用于临床检测、生化分析等领域。该文介绍了电化学酶联免疫传感器的概念与工作原理。根据检测换能器的不同进行了分类比较,并分别阐述了各种电化学酶联免疫传感器的工作原理与特点。综述了近年来常用于电化学酶联免疫传感器的标记酶及其在分析测试中的应用。     

The electrochemical method for detecting 26S proteasome

Detection of 26S proteasome, a multiproteolytic complex that degrades intracellular proteins in eukaryotic cells, by electrochemical methods is of interest for improved understanding of living cells and detection of cancer. This study develops an electrochemical system to detect 26S using a gold electrode modified by a self-assembled monolayer of 1,6-hexanedithiol (HDT) for capture of 26S proteasomes. When 26S is fixed on a HDT-gold electrode, it is found that electrolyte anions can enhance detection but also cause damage to the HDT layer. Cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that HDT stability is better in LiClO₄ solution than in sodium sulfate (Na₂SO₄) solution. Chymotrypsin-like activity of 26S as measured by fluorescence with Suc-LLVY-AMC substrate declines 10% with LiClO₄ and 25% with Na₂SO₄. LiClO₄ is a better electrolyte salt in a 26S-HDT-gold electrode application in Tris buffer. Increased electron transfer resistance is observed after binding 26S on the HDT-gold electrode. Stable 26S concentration is from 2 to 100 nM. As 26S concentration increases from 2 to 100 nM, the electron-transfer impedance of Fe(CN)₆^4−/3− redox rises logarithmically. The range of electrochemical detection of 26S proteasome is nanomolar.     

Sensitive PAT gene sequence detection by nano-SiO2/p-aminothiophenol self-assembled films DNA electrochemical biosensor based on impedance measurement

Nano-SiO₂/p-aminothiophenol (PATP) film was fabricated by self-assembly and electrodeposition methods. The immobilization and hybridization of DNA on the nano-SiO₂/PATP film were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was applied to label-free detection of the target DNA according to the increase of the electron transfer resistance (R_et) of the electrode surface after the hybridization of the probe DNA with the target DNA. This DNA electrochemical biosensor showed its own performance of simplicity, good stability, fine selectivity and high sensitivity, and was successfully applied to the detection of the PAT gene sequences by a label-free EIS method. The dynamic detection range was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol/L 20-base sequence of the PAT gene, with the detection limit of 1.5 × 10⁻¹² mol/L. This DNA sensor has a good ability of recognizing single- or double-base mismatched DNA sequence with the complementary DNA sequence.     

A PDMS microfluidic impedance immunosensor for E. coli O157:H7 and Staphylococcus aureus detection via antibody-immobilized nanoporous membrane

In this article, a PDMS microfluidic immunosensor integrated with specific antibody immobilized alumina nanoporous membrane was developed for rapid detection of foodborne pathogens Escherichia coli O157:H7 and Staphylococcus aureus with electrochemical impedance spectrum. Firstly, antibodies to the targeted bacteria were covalently immobilized on the nanoporous alumina membranes via self assembled (3-glycidoxypropyl)trimethoxysilane (GPMS) silane. Then, the impedance spectrum was recorded for bacteria detection ranging from 1 Hz to 100 kHz. The maximum impedance amplitude change for these two food pathogens was around 100 Hz. This microfluidic immunosensor based on nanoporous membrane impedance spectrum could achieve rapid bacteria detection within 2 h with a high sensitivity of 10² CFU/ml. Cross-bacteria experiments for E. coli O157:H7 and S. aureus were also explored to testify the specificity. The results showed that impedance amplitude at 100 Hz had a significant reduction in binding of bacteria when the membrane was exposed to non-specific bacteria.     

Novel approach for detection of toxic organophosphorus compounds

We report on a novel approach for the detection of toxic organophosphorus (OP) compounds using electrochemical and fluorescence spectroscopy. An electrochemical sensor device that employs gold (Au) interdigitated electrodes (IDT) on a glass substrate was used for the electrical impedance spectroscopy (EIS) of various OP compounds. Picomolar level detection of ethion, malathion, parathion and fenthion was made possible through EIS performed in the presence of benzodipyrido [3,2-a:2′3′-c] phenazine (BDPPZ). Quantitative detection of ethion, malathion, parathion and fenthion, based on different optical signals produced in the emission spectra, was obtained through fluorescence titration spectroscopy for concentrations as low as 1 pM, 1 nM, 1 μM and 10 μM, respectively.     

A Realtime and Continuous Assessment of Cortisol in ISF Using Electrochemical Impedance Spectroscopy

This study describes the functioning of a novel sensor to measure cortisol concentration in the interstitial fluid (ISF) of a human subject. ISF is extracted by means of vacuum pressure from micropores created on the stratum corneum layer of the skin. The pores are produced by focusing a near infrared laser on a layer of black dye material attached to the skin. The pores are viable for approximately three days after skin poration. Cortisol measurements are based on electrochemical impedance (EIS) technique. Gold microelectrode arrays functionalized with Dithiobis (succinimidyl propionate) self-assembled monolayer (SAM) have been used to fabricate an ultrasensitive, disposable, electrochemical cortisol immunosensor. The biosensor was successfully used for in-vitro measurement of cortisol in ISF. Tests in a laboratory setup show that the sensor exhibits a linear response to cortisol concentrations in the range 1 pm to 100 nM. A small pilot clinical study showed that in-vitro immunosensor readings, when compared with commercial evaluation using enzyme-linked immunoassay (ELISA) method, correlated well with cortisol levels in saliva and ISF. Further, circadian rhythm could be established between the subject's ISF and the saliva samples collected over 24 hours time-period. Cortisol levels in ISF were found reliably higher than in saliva. This Research establishes the feasibility of using impedance based biosensor architecture for a disposable, wearable cortisol detector. The projected commercial in-vivo real-time cortisol sensor device, besides being minimally invasive, will allow continuous ISF harvesting and cortisol monitoring over 24 hours even when the subject is asleep. Forthcoming, this sensor could be interfaced to a wireless health monitoring system that could transfer sensor data over existing wide-area networks such as the internet and a cellular phone network to enable real-time remote monitoring of subjects.     

Aptamer biosensor for label-free impedance spectroscopy detection of thrombin based on gold nanoparticles

This paper presents a simple electrochemical impedance spectroscopy (EIS) aptasensor based on an anti-thrombin-aptamer as a molecular recognition element. Improvement in sensitivity was achieved by utilizing gold nanoparticles (AuNPs), which were self-assembled on the surface of a bare electrode by using 1,6-Hexanedithiol as a medium. To quantify the amount of thrombin, changes in the interfacial electron transfer resistance (R_et) of the aptasensor were monitored using the redox couple of an [Fe(CN)₆]^3−/4− probe. The plot of (Reti−Ret₀)/Ret₀ against the logarithm of thrombin concentration is linear with over the range from 0.1 nM to 30 nM with a detection limit of 0.013 nM. Meanwhile, the packing density of aptamers was determined by cyclic voltammetric (CV) studies of redox cations (e.g., [Ru(NH₃)₆]³⁺) which were electrostatically bound to the DNA phosphate backbones. The results indicate that the total amount of aptamer probes immobilized on the gold nanoparticle surface is sixfold higher than that on the bare electrode. The aptasensor also showed good selectivity for thrombin without being affected by the presence of other proteins.     

A novel fluidic strain sensor for large strain measurement

A novel fluidic strain sensor is proposed with the use of a mixture of glycerin with aqueous sodium chloride encapsulated within an elastomer as a mean for piezoresistive large strain measurement. Electrochemical impedance spectroscopy (EIS) is conducted for strain response measurement and equivalent circuit analysis is applied for explaining the strain-affected ion transportation behavior of the sensor. The applied strain has caused an increase in both the resistance to charge transfer (R_ct) and the resistance of the salt solution which is reflected in an increase in the resistance of the system (R_sys). A parabolic relationship between the real part of the impedance (Z_re) and the true strain () for an applied strain of up to about 30% is verified. In addition, a novel fluid encapsulation technique by applying oxygen plasma surface modification is introduced. Aqueous sodium chloride is successfully encapsulated within an elastomeric casing with a pattern and this sensor is capable of measuring large strain of even up to about 40%. This method is suggested as an industrial fabrication technique for the strain sensor. The use of ionic liquids for green chemistry has been suggested for years and its use as an electrical conductive media in large strain sensor technology is found to be direct and environmentally friendly.     

Piezoresistance in chemically synthesized polypyrrole thin films

The resistance of chemically synthesized polypyrrole (PPy) thin films is investigated as a function of the pressure of various gases as well as of the film thickness. A physical, piezoresistive response is found to coexist with a chemical response if the gas is chemically active, like, e.g., oxygen. The piezoresistance is studied separately by exposing the films to the chemically inert gases such as nitrogen and argon. We observe that the character of the piezoresistive response is a function not only of the film thickness, but also of the pressure. Films of a thickness 70 nm show a decreasing resistance as pressure is applied, while for thicker films, the piezoresistance is positive. Moreover, in some films of thickness ≈70 nm, the piezoresistive response changes from negative to positive as the gas pressure is increased above ≈500 mbar. This behavior is interpreted in terms of a total piezoresistance which is composed of a surface and a bulk component, each of which contributes in a characteristic way. These results suggest that in polypyrrole, chemical sensing and piezoresistivity can coexist, which needs to be kept in mind when interpreting resistive responses of such sensors.     

Development of sulfhydrylated antibody functionalized microcantilever immunosensor for taxol

An immobilization method using a sulfhydrylated monoclonal antibody (mAb) on the gold surface of a microcantilever immunosensor was developed for label-free detection of taxol. The sulfhydrylated anti-taxol mAb was synthesized. Then it was immobilized on the gold surface of the microcantilever. The deflection of the microcantilever corresponding to different taxol concentrations was real time monitored by optical lever technique. The activity of the anti-taxol mAb before and after sulfhydrylation, and the binding of the sulfhydrylated anti-taxol mAb on the gold surface of the microcantilever were evaluated by non-competitive enzyme-linked immunosorbent assay (ELISA). The limit of detection is 1 ng/mL and the method was used for detection of taxol in human plasma sample.     

An ultra-sensitive chemiluminescence immunosensor of carcinoembryonic antigen using HRP-functionalized mesoporous silica nanoparticles as labels

A novel chemiluminescence immunosensor using horseradish peroxidase (HRP)-functionalized mesoporous silica nanoparticles (MSN) as labels was developed, which increases the sensitivity of the chemiluminescence immunoassay. The enzyme-functionalized MSN were fabricated by simultaneous coimmobilization of HRP and the carcinoembryonic antigen antibody (anti-CEA) onto the surface of MSN using 3-aminopropyltriethoxysilane (APTES) as the linkage. Because the large surface area of MSN carriers increased the amount of HRP bound per sandwiched immunoreaction, the conjugates provided a much higher signal and increased sensitivity. This is an improvement over the traditional sandwich immunoassay which often has one or two enzyme molecules per antibody. This approach was successfully demonstrated as a simple, cost-effective, specific, and potent method to detect CEA in practical samples. The analysis showed a linear response within the range of 0.1-40 ng/mL (r = 0.9912). The relative standard deviation (RSD) for 11 parallel measurements of 20 ng/mL CEA was 3.9%. The sensitivity of the immunosensor using MSN-HRP-Ab2 as labels was about 10-fold higher than that of traditional labels. These labels for immunosensors may provide many potential applications for detection of different biomolecules.     

电化学免疫传感器在环境污染监测中的研究进展

近年的研究以免疫识别与电子传递机制(如不同电子介体、直接电子传递)为核心,对于提高免疫识别信号与电化学信号的转换效率具有重要作用.IC工艺(如厚膜技术)制备免疫电极的方法,生物分子固定化技术以及多层膜结构,也在近年得到很大的发展,免疫电极的可靠性和实用性有了一定的改善.在电活性物质标记的基础上,电化学免疫传感器具有较高的灵敏度(如电流型传感器),也可以实时检测免疫反应(如电容型传感器).这类传感器具有较高灵敏度、操作简单和低成本的特点,适于环境监测(尤其是现场检测)技术要求,具有潜在的应用前景.在检测小分子半抗原(如杀虫剂)和病源微生物等方面都有了较大的发展.     

In situ three-dimensional analysis of the linear actuation of polypyrrole micro-rod actuators using optical microscopy

Polypyrrole (PPy) micro-rod actuators were electrochemically prepared into a porous polycarbonate (PC) by template synthesis. The linear actuation of the PPy micro-rod actuators at various potentials was consecutively monitored with in situ mode using an optical microscope (OM) and converted into 3-dimesional images. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and a potentiostat-galvanostat were used to confirm the actuation of PPy micro-rods during the redox process. Linear stretching actuation in the longitudinal dimension was successfully demonstrated.     

Analysis of response mechanism of a proton-pumping gate FET hydrogen gas sensor in air

Two different types of hydrogen response signals (DC and AC) of a proton-pumping gate FET with triple layer gate structure (Pd/proton conducting polymer/Pt) were obtained. The proton-pumping gate FET showed good selectivity against other gases (CH₄, C₂H₆, NH₃, and O₂). For practical use, the hydrogen response characteristics of the proton-pumping gate FET were investigated in air (a gaseous mixture of oxygen and nitrogen). The proton-pumping gate FET showed different hydrogen response characteristics in nitrogen as well as in air, despite the lack of oxygen interference independently. To clarify the response mechanism of the proton-pumping gate FET, a hydrogen response measurement was performed, using a gas flow system and electrochemical impedance spectroscopy. Consequently, the difference in response between nitrogen and air was found to be due to the hydrogen dissociation reaction and the interference with the proton transfer caused by the adsorbed oxygen on the upper Pd gate electrode.     

Impedimetric immunosensor for electronegative low density lipoprotein (LDL) based on monoclonal antibody adsorbed on (polyvinyl formal)-gold nanoparticles matrix

Monoclonal antibodies (MAb) have been commonly applied to measure LDL in vivo and to characterize modifications of the lipids and apoprotein of the LDL particles. The electronegative low density lipoprotein (LDL⁻) has an apolipoprotein B-100 modified at oxidized events in vivo. In this work, a novel LDL⁻ electrochemical biosensor was developed by adsorption of anti-LDL⁻ MAb on an (polyvinyl formal)-gold nanoparticles (PVF-AuNPs)-modified gold electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the recognition of LDL⁻. The interaction between MAb-LDL⁻ leads to a blockage in the electron transfer of the [Fe(CN)₆]⁴⁻/K₄[Fe(CN)₆]³⁻ redox couple, which may could result in high change in the electron transfer resistance (R_CT) and decrease in the amperometric responses in CV analysis. The compact antibody-antigen complex introduces the insulating layer on the assembled surface, which increases the diameter of the semicircle, resulting in a high R_CT, and the charge transferring rate constant κ⁰ decreases from 18.2 × 10⁻⁶ m/s to 4.6 × 10⁻⁶ m/s. Our results suggest that the interaction between MAb and lipoprotein can be quantitatively assessed by the modified electrode. The PVF-AuNPs-MAb system exhibited a sensitive response to LDL⁻, which could be used as a biosensor to quantify plasmatic levels of LDL⁻.     

电化学免疫法测定猪肉组织中青霉素的研究

将玻碳电极(GCE)表面氧化处理后,用戊二醛(GA)作交联剂,将新亚甲蓝(NMB)及辣根过氧化酶(HRP)标记的青霉素多克隆抗体(Abl修饰到电极表面,制成高灵敏电流型青霉素免疫传感器.通过循环伏安法考察了电极表面的电化学特性,并对猪肉中青霉素的残留进行了定量的研究.结果表明该传感器对猪肉中含有的青霉素检测的线性范围是5～50 ng,g,相关系数为0.977 9,检出限为2.45 ns/s.样品最高吸收率为69.4%.其中考查了蛋白沉淀刺的沉淀效果.发现运用三氯乙酸对猪肉中蛋白和脂类的沉淀效果最好.同时干扰性实验表明,交叉干扰较小.修饰的电极稳定性较好,可用于实际肉样中青霉素含量的测定.