Electrochemical behavior of thiamine on a self-assembled gold electrode and its square-wave voltammetric determination in pharmaceutical preparations.

The electrochemical behavior of thiamine on a self-assembled electrode of L-cysteine (Cys/SAM/Au) has been investigated and Cys/SAM/Au can be used to detect thiamine using square-wave voltammetry (SWV). At pH 11.40 Britton-Robinson buffer, thiamine exhibits a well-defined anodic peak on Cys/SAM/Au. Under the optimized conditions, the anodic peak current of SWV was linear with the content of thiamine in the range of 1.1 x 10(-8) - 2.2 x 10(-6) mol/L; the detection limit was 5.5 x 10(-9) mol/L. The method was successfully applied to the determination of thiamine in pharmaceutical preparations.     

Myoglobin/sol-gel film modified electrode: direct electrochemistry and electrochemical catalysis

Direct electrochemical and electrocatalytic behavior of myoglobin (Mb) immobilized on carbon paste electrode (CPE) by a silica sol-gel film derived from tetraethyl orthosilicate was investigated for the first time. Mb/sol-gel film modified electrodes show a pair of well-defined and nearly reversible cyclic voltammetric peaks for the Mb Fe(III)/Fe(II) redox couple at about -0.298 V (vs Ag/AgCl) in a pH 7.0 phosphate buffer solution. The formal potential of the Mb heme Fe(III)/Fe(II) couple shifted linearly with pH with a slope of 52.4 mV/pH, denoting that an electron transfer accompanies single-proton transportation. An FTIR and UV-vis spectroscopy study confirms that the secondary structure of Mb immobilized on an electrode by a sol-gel film still maintains the original arrangement. The immobilized Mb displays the features of a peroxidase and acts in an electrocatalytic manner in the reduction of oxygen, trichloroacetic acid (TCA), and nitrite. In comparison to other electrodes, the chemically modified electrodes used in this study for direct electrochemistry and electrocatalysis of Mb are easy to fabricate and fairly inexpensive. Consequently, the Mb/sol-gel film modified electrode provides a convenient way to perform electrochemical research on this kind of protein. It also has potential use in the fabrication of bioreactors and third-generation biosensors.     

Direct electrochemistry and electrocatalysis of myoglobin in dodecyltrimethylammonium bromide film modified carbon ceramic electrode

Direct electrochemistry and electrocatalysis of myoglobin（Mb） were studied with Mb immobilized on dodecyltrimethylammonium bromide（DTAB） film modified carbon ceramic（CC） electrode.Cyclic voltammetry showed a pair of well-defined and nearly reversible redox peaks of Mb（Fe^Ⅱ/Fe^Ⅲ） at about—0.3 V vs.SCE（pH = 6.98）.The currents of the redox peak were linear to scan rate,and rate constant（Ks） was estimated to be 3.03 s^-1.The formal potential（E°’） of Mb in the DTAB/CC electrodes shifted linearly with pH with a slope of -36.44 mV/pH,implying that the electron transfer between DTAB and CC electrodes is accompanied by proton transportation.The immobilized Mb exhibited excellent electrocatalytic response to the reduction of hydrogen peroxide（H₂O₂）.     

Enhanced Electrocatalytic Oxidation of Paracetamol at DNA Modified Gold Electrode

Cysteine monolayer has been assembled onto bare gold electrode (SAM/Au), and subsequently deoxyribonucleic acid (DNA) has been successfully immobilized at the SAM/Au electrode. The thus modified electrode is assigned DNA/SAM/Au. Modification steps of the electrode were followed electrochemically using K₄[Fe(CN₆)] electrochemical marker. Also, the build‐up of the modified electrode composition is followed using EDX and the crystallographic orientation is inspected using XRD. The electrochemical behavior of paracetamol (PC) at DNA/SAM/Au electrode is investigated. Interestingly, the sluggish irreversible behavior of PC at the bare gold electrode is converted to a quasi‐reversible one at DNA/SAM/Au electrode pointing to some interaction between the immobilized DNA and PC. The enhanced electrochemical behavior of PC at modified DNA/SAM/Au electrode is successfully used for a sensitive electrochemical determination of PC. Square wave voltammetry (SWV) was used for this purpose. The concentration of PC was in linear relation with the peak current at the optimum conditions within the range 10.0–110.0 μg mL^?1 with correlation coefficient (R²) of 0.998. Also, the standard deviation (SD) and relative standard deviation (RSD) were calculated and found to be 0.817 and 1.52, respectively, indicating the significance of the present method.     

Mediator free cholesterol biosensor based on self-assembled monolayer platform

Self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) has been investigated for immobilization of bi-enzymes (ChOx and ChEt) towards development of enzyme biosensors for detection of free and total cholesterol. This enzyme immobilized SAM surface has been characterized by scanning electron microscopy and electrochemical measurements. The results of electrochemical response studies reveal fast enzymatic reaction in phosphate buffer saline solution without using any artificial mediator. This may be attributed to the molecular wire type behavior of short 4-ATP molecule that promotes electron transfer between enzyme and the electrode surface due to its conjugated structure. Interference free estimation of free and total cholesterol has been realized at low operating potential of 0.33 V with range of detection as 25 to 400 mg dl(-1), sensitivity of 542.3 nA mM(-1) (for ChOx/4-ATP/Au) and 886.6 nA mM(-1) (for ChEt-ChOx/4-ATP/Au) with a response time of 20 s at pH 7.4.     

Electrochemical and Electrocatalytic Properties of Ferrocene Incorporated in L‐Cysteine Self‐Assembled Monolayers on a Gold Electrode

Abstract

The preparation of a gold electrode modified by aminylferrocene (FcAI) covalently bound to L‐cysteine self‐assembled monolayer (L‐Cys/Au SAM) was described, and characterized by cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS). In pH 7.4 buffers, FcAI incorporated in L‐Cys/Au SAM gave a pair of well‐defined and quasi‐reversible cyclic voltammetric peaks at 0.109 vs. saturated calomel eletrode (SCE), characteristic of Fe(II)/Fe(III) redox couples of the Fc. The apparent surface electron transfer rate constant is 6.86 s^?1 at the modified electrode. The immobilized Fc gave an excellent electrocatalytic activity for the oxidation of epinephrine (EP). The catalytic current of EP vs. its concentration has a good linear relation in the range of 1.7×10^?7–1.0×10^?4 mol/L, with the correlation coefficient of 0.9975 and detection limit of 1.8×10^?8 mol/L. The modified electrode can be used for the determination of EP in practical injection. The method is simple, quick, sensitive, and accurate.     

还原聚苯胺插层氧化石墨纳米材料修饰电极用于抗坏血酸测定的研究

本文研制成还原聚苯胺插层氧化石墨纳米材料(R-(PAI/GO))修饰电极,并用于测定抗坏血酸(AA)。在pH5.02的Brinton-Robinson(B-R)缓冲溶液中,AA可在R-(PAI/GO)修饰电极上产生一对氧化还原峰,该峰的峰电流与AA浓度的对数在1.0×10-9~4.24×10-2mol/L范围呈良好的线性关系,相关系数为0.9910。多巴胺(DA)等物质对AA的测定无干扰。该电极制作简单,有良好的稳定性和重现性,用于实际试样中AA的测定,结果满意。     

基于微机电系统技术和纳米金自组装膜的安培型免疫传感器研究

基于微机电系统(MEMS)技术制备安培型免疫传感器,并利用基于硫醇单层膜的纳米金单层膜自组装技术设计传感器界面,用于固定人免疫球蛋白(IgG)抗体,研制了一种新型的安培型免疫传感器。采用MEMS技术,在硅片上制备微型的三电极系统以及SU-8反应池。基于自组装技术,先在金电极上自组装巯基乙胺单层膜,利用膜上氨基与纳米金共价结合组装纳米金单层膜,得到可用于固定抗体的界面。实验探讨了影响抗体固定的主要实验参数和条件;考察了采用此固定化方法传感器的响应性能,与金电极直接吸附固定法和戊二醛共价交联固定法进行了比较。对IgG检测的实验结果表明,采用纳米金自组装膜固定抗体,具有活性高、非特异性吸附小、检测线性范围宽等优点。并且,基于MEMS技术的安培型免疫传感器具有微型化、与集成电路工艺相兼容、易于实现传感器的阵列化和实时多参数检测等优点。     

Selective determination of 3,4-dihydroxyphenylacetic acid in the presence of ascorbic acid using 4-(dimethylamino)pyridine capped gold nanoparticles immobilized on gold electrode

4-(Dimethylamino)pyridine capped gold nanoparticles (DMAP-AuNPs) were synthesized in aqueous medium and then immobilized on 1,6-hexanedithiol (HDT) modified Au electrode for the selective determination of 3,4-dihydroxyphenylacetic acid (DOPAC) in the presence of ascorbic acid (AA). The synthesized DMAP-AuNPs were characterized by UV-visible spectroscopy and high resolution-transmission electron microscopy (HR-TEM). The HR-TEM images showed that the nanoparticles are spherical in shape with a diameter of ～12 nm. The DMAP-AuNPs immobilized on HDT modified electrode was characterized by cyclic voltammetry and impedance spectroscopy. Impedance spectra show that the electron transfer reaction was more facile at the AuNPs modified electrode when compared to bare and HDT modified Au electrodes. The application of DMAP-AuNPs modified electrode was demonstrated by selective determination of DOPAC in the presence of high concentration of AA at pH 4. Using amperometry method, 40 nM detection of each AA and DOPAC was achieved. The current response was increased linearly with increasing AA and DOPAC in the concentration range of 40×10(-9) to 10×10(-5) M and a detection limit was found to be 5.6×10(-10) M and 3.7×10(-10) M (S/N=3) for AA and DOPAC, respectively. The present modified electrode was also successfully used for the determination of 40 nM DOPAC in the presence of 2500-fold excess of common interferents such as Na(+), Mg(2+), Cu(2+), Ca(2+), NH(4)(+) urea and glucose.     

Voltammetric Study of Methylene Blue at Thiol SAMs‐Modified Gold Electrodes

The voltammetric behavior of methylene blue (MB) at thiol self‐assembled monolayers modified gold electrodes (SAMs/Au) has been investigated. MB exhibited a redox peak at about ?0.35 V (vs.SCE) in alkaline solution at bare gold electrodes. When the gold electrodes were modified with thiol SAMs, the peak grew due to the accumulation of MB at SAMs. With the solution pH rising, more MB was accumulated, hence the peak height increased, which differed from that at bare gold electrodes. The electrode process at SAMs/Au featured the characteristics of adsorption and/or electrode reaction controlled. The enhancing action of glutathione monolayer (GSH SAM), 3‐mercaptopropionic acid monolayer (3MPA SAM) and other thiol SAMs was compared. Among these, GSH SAM made the MB peak increase more. At GSH SAM/Au, the peak height varied linearly with MB concentration over the range of 2 μM to 400 μM. So this can be developed for the determination of MB and studies concerned. The accumulation behavior caused by GSH SAM and native fish sperm dsDNA was compared. The interaction between DNA and MB was also discussed under this condition.     

Electrochemical behavior of the bis(2,2'-bipyridyl)copper(II) complex immobilized on a self-assembled monolayer modified electrode for L-ascorbic acid detection

Modification of a gold electrode has been achieved by immobilizing a bis(2,2'-bipyridyl)copper(II) complex in a self-assembled monolayer (SAM) of 3-mercaptopropionic acid. The electrostatic interaction of the negatively charged SAM with a di-positive copper complex allowed the attachment. The modified electrode exhibited excellent redox behavior. The dependence of the modified electrode response was investigated in terms of pH, supporting electrolyte and ionic strength. Moreover, it showed good electrocatalytic activity for ascorbic acid oxidation, allowing convenient quantification at levels down to 8.1 x 10(-8) mol l(-1). The [Cu(bipy)2]/SAM modified electrode under optimized operational conditions (PIPES buffer 0.01 mol l(-1) at pH 6.8 and 200 mV vs. SCE) presented a linear response range between 1.0 micromol l(-1) and 100.0 micromol l(-1) for ascorbic acid. This modified electrode also presented an excellent repeatability, showing a relative standard deviation of 2.1% for a series of 12 successive measurements of a 5.0 micromol l(-1) ascorbic acid solution. Furthermore, the electroactivity was maintained over a long period (e.g., 92% after 100 determinations).     

Direct electrochemistry and Raman spectroscopy of sol-gel-encapsulated myoglobin

The direct electrochemistry of myoglobin (Mb) has been observed at a glassy carbon (GC) electrode coated with silica sol-gel-encapsulated Mb film. A well-behaved cyclic voltammogram is observed with a midpoint potential (E(1/2)) of -0.25 V vs Ag/AgCl in a pH 7.0 phosphate buffer. This potential, which is pH-dependent, is 70-90 mV more negative than the formal potential values obtained by using the spectroeletrochemical titration method at the same pH. Square wave voltametry (SWV) also shows a peak potential of -0.25 V for the reduction of Mb under the same experimental conditions. Both cathodic and anodic peak currents have a linear relationship with the scan rate. The midpoint potential decreases with pH, having a slope of -30 mV/pH. UV-vis and resonance Raman spectroscopic studies reveal that the sol-gel provides a bio-compatible environment where Mb retains a structure similar to its solution form, a 6-coordinated aquomet myoglobin. These results suggest that the silica sol-gel is a useful matrix for studying direct electrochemistry of other heme proteins.     

PCA/GC电极同时测定尿酸(UA)和抗坏血酸(AA)

制备聚肉桂酸(PCA)修饰电极(PCA/GC),研究尿酸(UA)和抗坏血酸(AA)在该电极上的电化学行为.结果表明,在UA和AA共存体系中,UA、AA在PCA/GC电极上氧化峰电流增大且峰电位分别负移至50mV、330mV,二者相差280mV,据此可同时检测UA和AA.在pH6.0磷酸盐缓冲液中,UA、AA的氧化峰电流与其浓度分别在2.0×10-6～1.0×10-4mol·L-1、2.0×10-5～6.0×10-4mol·L-1范围内呈线性关系.该电极重现性好,适用于尿样中UA的检测.     

肌红蛋白-纳米氧化铝模板-金胶复合组装体的直接电化学与电催化

将肌红蛋白(Mb)固定在纳米氧化铝(AAO)模板-金胶复合组装体修饰玻碳电极表面,制得Mb/AAO/Au colloid/GC薄膜电极.在pH=5.4的HAc-NaAc缓冲溶液中,该薄膜电极于-0.21 V(vs.Ag/AgC l)处有一对准可逆的氧化还原峰,为Mb血红素辅基Fe(Ⅲ)/Fe(Ⅱ)电对的特征峰.在AAO/Au colloid薄膜的微环境中,Mb与玻碳电极间的电子传递明显加快,该Mb/AAO/Au colloid/GC薄膜电极还可用于过氧化氢和溶解氧的催化还原.     

Efficient Electrocatalytic Detection of Epinephrine at Gold Electrodes Modified with Self‐Assembled Metallo‐Octacarboxyphthalocyanine Complexes

Electrocatalysis of epinephrine at gold electrode pre‐modified with the self‐assembled monolayer of cysteamine and subsequently integrated with novel metallo‐octacarboxyphthalocyanine (MOCPc where M=Fe, Co and Mn) complexes (Au‐Cys‐MOCPc) was investigated. The electrodes showed response to the presence of epinephrine. The oxidation peak potential (E_p/V vs. Ag|AgCl, sat'd KCl) and charge transfer resistance (R_ct (kΩ)) in epinephrine solution depend markedly on the central metal of the phthalocyanine cores: Au‐Cys‐FeOCPck_ch=4.1×10⁷ M^?1 s^?1) which is higher than that of the Au‐cys‐CoOCPc or Au‐cys‐MnOCPc electrode. Mechanism, recognizing the mediation of the electrocatalytic process by the central M(II)/M(III) redox processes was proposed. Epinephrine electro‐oxidation at the Au‐cys‐FeOCPc electrode was studied in more details for the response characteristics. The diffusion coefficient of epinephrine was evaluated as (2.62±0.23)×10^?9 cm² s^?1. It was established that Au‐Cys‐FeOCPc is suitable for sensitive determination of epinephrine in physiological pH (7.40) conditions showing linear concentration range of up to 300 nM, with excellent sensitivity (0.53±0.01 nA nM^?1), and very low limits of detection (13.8 nM) and quantification (45.8 nM). The peak separation between ascorbic acid and epinephrine is large enough (190 mV) to permit simultaneous determination of both epinephrine and ascorbic acid in physiological pH 7.4 conditions using the Au‐cys‐FeOCPc electrode. Au‐cys‐FeOCPc electrode was successfully used for the determination of epinephrine in epinephrine hydrochloric acid injection with recovery of ca. 98.4%.     

Mb/AuNPs/MWCNTs/GC电极对H2O2电催化性能的研究

采用还原法制备了AuNPs/MWCNTs复合材料,并构建了氧化还原蛋白质的固定化和生物传感界面AuNPs/MWCNTs/GC电极.以肌红蛋白(Myoglobin,Mb)为例,研究了固定化蛋白质在AuNPs/MWCNTs/GC电极上的直接电化学.结果表明,AuNPs/MWCNTs复合材料不仅能有效地促进Mb与电极表面的直接电子转移,而且能很好地保持固定化Mb的生物催化活性.Mb/AuNPs/MWCNTs/GC电极对H2O2具有良好的电催化还原性能,其线性响应范围为1～138μmol·L-1,检测限为0.32μmol·L-1(S/N=3),并具有较低的米氏常数(0.143 mmol·L-1).该电极操作简单,响应迅速,稳定性和重现性好,有望用于蛋白质的固定化及第三代生物传感器的制备.     

Electrodeposited nanogold decorated graphene modified carbon ionic liquid electrode for the electrochemical myoglobin biosensor

In this paper, a carbon ionic liquid electrode (CILE) was fabricated using ionic liquid 1-hexylpyridinium hexafluorophosphate as modifier, which was further in situ electrodeposited with graphene (GR) and gold nanoparticles step by step to get an Au/GR nanocomposite modified CILE. Myoglobin (Mb) was further immobilized on the Au/GR/CILE surface with Nafion film to get the modified electrode denoted as Nafion/Mb/Au/GR/CILE. Cyclic voltammetric experiments indicated that a pair of well-defined quasi-reversible redox peaks appeared in pH 3.0 phosphate buffer solution with the formal potential (E ^0′) located at ?0.197 V (vs. saturated calomel electrode), which was the typical characteristics of Mb heme Fe(III)/Fe(II) redox couples. Thus, the direct electron transfer rate between Mb and the modified electrode was promoted due to the high conductivity and increased surface area of Au/GR nanocomposite present on electrode surface. Based on the cyclic voltammetric data, the electrochemical parameters of Mb on the modified electrode were calculated. The Mb-modified electrode showed excellent electrocatalytic activities towards the reduction of trichloroacetic acid and H₂O₂ with wider linear range and lower detection limit. Using GR and Au nanoparticles modified CILE, a new third-generation electrochemical Mb biosensor was constructed with good stability and reproducibility.     

Direct electrochemistry and electrochemical catalysis of myoglobin-TiO2 coated multiwalled carbon nanotubes modified electrode

TiO(2) nanoparticles were homogeneously coated on multiwalled carbon nanotubes (MWCNTs) by hydrothermal deposition, and this nanocomposite might be a promising material for myoglobin (Mb) immobilization in view of its high biocompatibility and large surface. The glassy carbon (GC) electrode modified with Mb-TiO(2)/MWCNTs films exhibited a pair of well-defined, stable and nearly reversible cycle voltammetric peaks. The formal potential of Mb in TiO(2)/MWCNTs film was linearly varied in the range of pH 3-10 with a slope of 48.65 mV/pH, indicating that the electron transfer was accompanied by single proton transportation. The electron transfer between Mb and electrode surface, k(s) of 3.08 s(-1), was greatly facilitated in the TiO(2)/MWCNTs film. The electrocatalytic reductions of hydrogen peroxide were also studied, and the apparent Michaelis-Menten constant is calculated to be 83.10 microM, which shows a large catalytic activity of Mb in the TiO(2)/MWCNTs film to H(2)O(2). The modified GC electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant Mb-TiO(2)/MWCNTs modified glassy carbon electrode exhibited fast amperometric response to hydrogen peroxide reduction, long term life and excellent stability. Finally the activity of the sensor for nitric oxide reduction was also investigated.     

High Sensitive Detection of Prostate Specific Antigen by Using Ferrocene Cored Asymmetric PAMAM Dendrimer Interface Screen Printed Electrodes

In this study, electrochemical immunosensors were developed for the detection of prostate specific antigen (PSA) using ferrocene (Fc) and polyamidoamine dendrimer (PAMAM) constructs. The biosensor fabrication was designed by modifying the screen‐printed gold electrode (Au) with ferrocene cored dendrimers (FcPAMAM) synthesized in three different generations. The self‐assembled monolayer principle was followed, to obtain sensitive, selective and disposable electrodes. Therefore, the Au electrodes were modified with cysteamine (Cys) to obtain a functional surface for FcPAMAM dendrimers to bind. Dendrimer generations were attached to this surface using a cross‐linker (glutaraldehyde) so that a suitable surface was obtained for binding of biological components. The Monoclonal PSA antibody (anti‐PSA) was immobilized on the Au electrode surface which coated with dendrimer, and (Au/Cys/FcPAMAM/anti‐PSA) biosensing electrode was obtained. The PSA detection performances of electrochemical impedance spectroscopy (EIS) and Amperometry based immunosensors exhibited very low detection limits; 0.001 ng mL^?1 and 0.1 pg mL^?1, respectively. In addition, EIS and Amperometry based biosensors using Au/Cys/FcPAMAM/anti‐PSA sensing electrode were represented excellent linear ranges of 0.01 ng mL^?1 to 100 ng mL^?1 and 0.001 ng mL^?1 to 100 ng mL^?1. In order to determine the applicability recovery and selectivity tests were performed using three different proteins in human serum.     

Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl‐dopa and Ascorbic Acid

A novel voltammetric method using the Ppyox/NFR/Au (poly pyrrole – nuclear fast red – gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Polypyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the electropolymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV) method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the measurement of both analytes using modified electrode. Well‐separated voltammetric peaks were observed for ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0×10^?6 to 1.0×10^?3 and 1.0×10^?7 to 2.0×10^?5 mol L^?1 respectively. The detection limit of 5.8×10^?6 and 5.0×10^?8 mol L^?1 (S/N=3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA and MDA in some real samples such as human serum and tablet.