Electrochemical Oxidation of Donepezil and Its Voltammetric Determination at Gold Electrode

The oxidative ability of donepezil, a frequently prescribed drug for the treatment of Alzheimer’s disease is reported for the first time at a gold electrode. It was oxidized by cyclic voltammetry and determined by square wave voltammetry in phosphate buffer electrolyte. Electrochemical degradation of donepezil was carried out by long term potential cycling. The identification and characterization of the major product, isolated by preparative high performance liquid chromatography, was performed by high resolution mass spectrometry and 1D and 2D nuclear magnetic resonance spectroscopy. Donepezil hydroxy derivative was identified as the major electrochemical oxidation product from donepezil.     

葡萄糖在纳米金修饰金电极上电化学行为研究

利用电还原氯金酸制备了纳米金(Nano-gold,NG)修饰Au电极。该电极对葡萄糖有催化作用,可能是由于纳米金降低了OH-表面吸附能,增加了OH-在电极表面的吸附量。通过循环伏安法研究了扫描速度、温度、本体浓度和溶液pH值对葡萄糖氧化的影响。     

吸附方波伏安法研究单偶氮化合物表面电化学反应

在静止汞滴电极上用吸附方波伏安法研究了9个单偶氮化合物的表面电化学反应,观察到3种类型的方波伏安图,其中两类可用提出的4电子二步还原反应机理解释。第一步为准可逆还原,第二步为完全不可逆。第三种类型的伏安图可解释为4电子一步还原。以这两种反应机理为数学模型,用非线性最小二乘法分析实验伏安图,理论曲线与实验曲线吻合极好。获得了各偶氮化合物表面电化学反应的动力学参数,初步归纳出反应机理与取代基的关系,为研究其在生物体内的降解反应及致癌性提供了有参考价值的化学信息。     

A Novel Adsorptive Square Wave Voltammetric Method for Pico Molar Monitoring of Lorazepam at Gold Ultra Microelectrode in a Flow Injection System by Application of Fast Fourier Transform Analysis

Abstract

This paper describes development of a new analysis system for determination of lorazepam by a novel square wave voltammetry method to perform a very sensitive method. The method used for determination of lorazepam involves measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 M H₃PO₄ solution) caused by adsorption of the lorazepam on the electrode surface. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorbed lorazepam. Furthermore, signal-to-noise ratio is significantly increased by application of discrete fast Fourier transform (FFT) method, background subtraction, and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work, some parameters such as SW frequency, eluent pH, and accumulation time were optimized. Calibration plots are given for solutions containing 10^?6–10^?11 M of lorazepam. The detection limit is calculated to be 6.0 × 10^?12 M (～ 2 pg/ml). The relative standard deviation at concentration 3.0 × 10^?8 M is 6.1% for 5 reported measurements.     

Direct Electrochemical Oxidation of DNA on Polycrystalline Gold Electrodes

Electrochemical CV and SWV studies were performed with double stranded DNA from salmon testes (dsDNA) and single stranded DNAs, containing 25 nucleotides (ssDNA) directly adsorbed at polycrystalline Au electrodes. A distinct oxidation peak at +730 mV (SWV, scan rate 0.248 V s^?1) or at +730 – +780 mV (CV, scan rate from 0.3 to 1 V s^?1) was obtained with DNA‐modified Au electrodes after a time‐dependent prepolarization step at a positive potential value, i.e., at +500 mV (vs. Ag|AgCl), performed with the DNA‐modified Au electrodes dipped in a blank buffer solution. No electrochemical activity was detected when ssDNA, containing no guanines, was used for adsorptive modification of the Au electrodes. Electrochemical impedance measurements registered a possible reorganization of the adsorbed DNA layer in the course of the prepolarization, accompanied by decreasing in‐phase impedance. The results enable us to relate the oxidation process observed at the DNA‐modified Au electrodes with the oxidation of guanine residues in DNA.     

手性药物心得安对映体的毛细管电泳/电化学分离检测研究

报道了采用毛细管电泳 -方波安培检测法对手性药物对映体———外消旋心得安进行了分离检测研究。以5mmol/LNaOH -8mmol/L柠檬酸 -10mmol/Lβ_CD(pH4.5)为电泳介质 ,未涂层熔融石英毛细管(75μm×45cm)为分离通道 ,分离电压 +12.5kV ,实现了心得安对映体的基线分离。方法的线性范围为2.0×10 -6～1.0×10 -4mol/L ,检出限为5.0×10 -7mol/L。     

Non‐Enzymatic Electrochemical Detection of Glucose with a Gold Nanowire Array Electrode

High‐performance electrodes for in vivo electrochemical detection of glucose (GO) are highly desirable. In this work, we propose a new approach to efficiently and precisely prepare a Au nanowire array electrode (ANAE) with a line width of 78 nm and a large sensor area of 60 mm×60 mm for GO detection. In this approach three techniques, i.e., vacuum sputtering‐deposition, holography photolithography, and argon ion‐beam etching, are integrated. The fabricated ANAE exhibits good performance for GO detection. A linear amperometric response to the oxidation of GO in a concentration range of 0.4–10 mM is observed. The ANAE is characterized by its high detection sensitivity, selectivity, stability and good biocompatibility. All of these make it a promising tool for GO detection and other relevant applications.     

方波伏安法测定食盐中的碘酸根离子

报道了一种测定碘酸根离子含量的方法。在 0 .5mol/L Na Cl介质中 ,碘酸根离子在汞膜电极上于 - 1 .2 5V( vs.Ag/Ag Cl)左右产生一灵敏的方波伏安峰 ,峰高与碘酸根离子浓度在一定范围内呈良好的线性关系 ,方法检出限为1 .0× 1 0 - 7mol/L,已用于加碘食盐中碘酸根含量的测定。     

Amperometric Glucose Biosensor Based on Electrochemically Deposited Gold Nanoparticles Covered by Polypyrrole

Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy‐layer formation and the linear interval was extended up to 19.9 mmol L⁻¹ after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM⁻¹ cm⁻², the limit of detection – 0.20 mmol L⁻¹. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t _1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples.     

方波悬汞吸附伏安法测定八氧化三铀中的钛

U_3O_3用HNO_3溶解,用TBP萃淋树脂分离铀,水溶液用HClO_4蒸干,残渣溶于10ml、pH=6.1的0.1mol/L EDTA、lmol/L的NaAc溶液中,加入1％铜铁试剂0.5ml,于-0.6V～-1.1V的电位范围内用方波伏安法测定钛。标准偏差约为5％,最低检出限为0.5ng/ml。     

A Simple,Efficient and Ultrasensitive Gold Nanourchin Based Electrochemical Sensor for the Determination of an Antimalarial Drug: Mefloquine

Mefloquine (MQ) is a quinoline based antimalarial drug, which is potent against multiple drug‐resistant Plasmodium falciparum . It is widely prescribed for the prophylactic treatment of malaria. Due to extensive usage of MQ, constant monitoring of the drug level in human body is of paramount importancein order to ensure that optimum drug exposure is achieved. The present work describes a gold nanourchins (AuNUs) based electrochemical sensor for the determination of MQ.AuNUs were synthesized via seed‐mediated method and characterized using ultraviolet‐visible spectroscopy, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, zeta‐sizer and electrochemical techniques (electrochemical impedance spectroscopy and cyclic voltammetry). Fabrication of the sensor was done by drop‐coating the synthesized AuNUs onto a glassy carbon electrode. The fabricated sensor exhibited enhanced voltammetric response, which was attributed to the excellent conductivity and high surface area of AuNUs. Under optimum square wave voltammetric conditions, the sensor displayed two linear response ranges (from 2.0×10⁻⁹ to 1.0×10⁻⁶ M and from 1.0×10⁻⁶ to 1.0×10⁻³ M) with a detection limit of 1.4 nM. The electrode demonstrated good reproducibility, stability and selectivity over common interferents. The utility of the sensor was successfully assessed for quantification of the drug in pharmaceutical preparation and spiked human urine sample. Thus, the present study demonstrates a promising approach for determination of MQ with practical utility in quality control and clinical analysis.     

Tannic Acid Modified Electrochemical Biosensor for Glucose Sensing Based on Direct Electrochemistry

A novel glucose biosensor was constructed through the immobilization of glucose oxidase (GOx) on gold nanoparticles (Au NPs) deposited, and chemically reduced graphene oxide (rGO) nanocomposite. In the synthesis, tannic acid (TA) was used for the reduction of both graphene oxide, and Au³⁺ to rGO, and Au NPs, respectively. Also, by harnessing the π‐π interaction between graphene oxide and TA, and protein‐TA interaction, a novel nanocomposite for the fabrication of a third generation biosensor was successfully constructed. Upon the oxidation of TA to quinone, which is easily reducible at the negative potential range, enhanced electron transfer was obtained. The cyclic voltammetry (CV) results demonstrated a pair of well‐defined and quasi‐reversible redox peaks of active site molecule of GOx. The biosensor exhibited a linear response to glucose concentrations varying from 2 to 10 mM with a sensitivity of 18.73 mA mM⁻¹ cm⁻². The fabricated biosensor was used for the determination of glucose in beverages.     

基于聚对苯二甲酸乙二醇酯薄膜的石墨烯/金纳米粒子/葡萄糖氧化酶柔性电极的制备及检测葡萄糖

采用化学气相沉积法生长多晶石墨烯(Graphene, G),转移至聚对苯二甲酸乙二醇酯(PET)薄膜表面,通过控制金溶胶蒸发速率,在多晶石墨烯表面组装均匀分布的亚单层金纳米粒子(AuNPs);然后修饰巯基乙酸,通过共价交联反应将葡萄糖氧化酶固定于AuNPs表面,构建基于PET膜的石墨烯/金纳米粒子/葡萄糖氧化酶(G/AuNPs/GOD)柔性电极.此电极在工作电位0.6 V(vs.SCE电极)、pH 7.0磷酸盐缓冲溶液、室温25℃条件下,差分脉冲伏安法响应电流与被测葡萄糖浓度在0.05~10.55 mmol/L范围内呈线性关系,线性方程为I(108A)=0.2629 C(mmol/L)+1.4149,线性相关系数 r=0.9955,检出限1 μmol/L (3σ). G/AuNPs/GOD柔性电极的制备可为特定环境和可穿戴设备的葡萄糖检测提供了新的途径和方法,拓展了葡萄糖检测的应用范围.     

Electrochemical response of oligonucleotides on carbon paste electrode

Electrochemical response of synthetic oligonucleotides with different DNA bases sequences was investigated to find relationships between a chain composition and a signal. All DNA mononucleotides present electroactivity at a carbon paste electrode yielding anodic peaks at potentials: 1.00 (GMP), 1.28 (AMP), 1.47 (TMP) and 1.53 V (CMP). Also 15-mer homooligonucleotides show respective anodic peaks. Electrochemical response of 15- and 19-mer oligonucleotides consisting of all four DNA bases in different amounts was determined by the composition of oligonucleotide chain. When the contribution of different bases in oligonucleotide was balanced two anodic peaks were obtained that can be attributed to guanine and adenine moieties. Thymine residue is shown as a separate peak in voltammogram when its content in oligonucleotide chain is close to 50% of the total number of bases. Cytosine also yields a peak at its significant contribution in oligonucleotide chain and both pyrimidinic moieties produce catalytic waves easier when one of them is dominating or when only one pyrimidine derivative is present in a chain. Guanine is the easiest oxidized base and it produces a peak even at its minimal contribution (one guanine residue in 19-mer oligonucleotide). Guanine peak potential is dependent on oligonucleotide concentration and oligonucleotide composition. The lowest oligonucleotide concentration detected by guanine peak was 12.5 nM whereas detected by thymine peak was 90 nM.     

Square Wave Electroanalysis at Generator–Collector Gold–Gold Double Hemisphere Junctions

Gold–gold double‐hemisphere junction electrodes with an inter‐electrode gap of typically 1 µm are employed for generator–collector square wave voltammetry. Electrochemical data are recorded as a function of both generator and collector potential to give three‐dimensional response “maps”. At sufficiently low frequencies, close‐to‐steady‐state conditions for the collector response are achieved and peak responses complementary to those for the generator electrode are recorded. Due to localised interelectrode gap diffusion (fast) as opposed to peripheral diffusion (slow), information about reaction products and intermediates can be obtained. Local pH gradient effects provide additional “fingerprint” information beneficial for future application in analytical detection.     

Assembly of Glucose Oxidase and Different Polyelectrolytes by Means of Electrostatic Layer‐by‐Layer Adsorption on Thiolated Gold Surface

A rational strategy for the construction of a bioelectrocatalytic architecture by means of alternate electrostatic adsorption is described. Multilayer films containing glucose oxidase (GOx) and different polyelectrolytes were assembled onto a thiolated‐gold surface and the resulting bioelectrode was used for glucose biosensing. The supramolecular multistructure was prepared by assembling polyethylenimine and Nafion (as anti‐interference barrier), followed by the adsorption of polyethylenimine and DNA (as stabilizing film) and finally by the alternate deposition of polyethylenimine and glucose oxidase (as a biocatalytic layer). The influence of the deposition time and concentration of polyelectrolytes, organization and number of layers on the sensitivity and selectivity of the bioelectrode is discussed. The resulting enzymatic biorecognition layer exhibits very good analytical performance with a fast, sensitive (3.3±0.1)×10⁴ nA M^?1 and highly selective (0% interference for 6.0 mg % uric acid and 2.0×10^?4 M ascorbic acid) response to glucose, demonstrating that the alternate electrostatic adsorption of conveniently selected polyelectrolytes allow a large improvement in the selectivity and sensitivity of a biosensor.     

Electrochemical Oxidation and Determination of Glucose Using Cyclic Voltammetry and a One‐step Prepared Nanoporous Gold Wire Electrode

A nanoporous gold wire electrode (NPGWE) was prepared using a published one‐step method from a 0.3 M oxalic acid at room temperature. It was found in this study that the surface morphology, including the pore size and the width of the ligaments, and thus the surface roughness of the NPGWE could be easily manipulated by controlling the solution stirring rate. The NPGWE was used for the study of electrochemical oxidation and determination of glucose in 0.1 M NaOH using cyclic voltammetry. The effect of two potential interferences chloride ion and ascorbic acid was assessed. The electrode showed a linear range of glucose concentration from 0.5 mM to 10 mM with a detection limit of 8 μM.     

Advances in the Study of Ion Transfer at Liquid Membranes with Two Polarized Interfaces by Square Wave Voltammetry

A general analytical expression has been deduced for the I/E response of the square wave voltammetry corresponding to ion transfer processes in systems with two liquid/liquid polarized interfaces. This expression has been evaluated through the experimental study of a series of quaternary ammonium cations and metal chloro complex anions. We have found that systems with two liquid/liquid polarizable interfaces present the striking advantage that the difference between peak potentials of square wave voltammograms of cations and anions with similar standard ion transfer potential is much greater than in systems with a single polarizable one.     

吸附方波伏库仑法研究 Ⅱ络合吸附体系

对络合吸附体系分别推导了前行化学反应平衡常数Ｋ１和Ｋ１两种情况的方波伏库仑法的电量方程及作了实验验证，获得判别这两种络合吸附体系的理论依据。讨论了各种因素对伏库仑曲线的影响，并由实验比较了方波伏库仑法和方波伏安法的检测限。     

Amperometric Glucose Biosensing of Gold Nanoparticles and Carbon Nanotube Multilayer Membranes

A novel multilayer gold nanoparticles/multiwalled carbon nanotubes/glucose oxidase membrane was prepared by electrostatic assembly using positively charged poly(dimethyldiallylammonium chloride) to connect them layer by layer. The modification process and membrane structures were characterized by atomic force microscopy, scanning electron microscopy and electrochemical methods. This membrane showed excellent electrocatalytic character for glucose biosensing at a relatively low potential (?0.2 V). The K_m value of the immobilized glucose oxidase was 10.6 mM. This resulting sensor could detect glucose up to 9.0 mM with a detection limit of 128 μM and showed excellent analytical performance.