Nanoporous Gold Leaf for Amperometric Determination of Nitrite

Ultra‐thin free‐standing nanoporous gold leaf made by dealloying exhibits excellent electrocatalytic activities toward nitrite oxidation. The electrochemical responses of nitrite ions on this novel nano‐electrode is found not dependent on pH over a wide range from 4.5 to 8.0, which is markedly different from that of gold oxidation, a process known to be highly pH‐sensitive. Amperometric study shows a linear relationship for nitrite determination in a concentration range from 1 µM to 1 mM. This nanostructured gold electrode displays good stability, repeatability and selectivity which suggests its potential for the development of new electrochemical sensors.     

Oxygen Evolution Reaction on Nanoporous Gold Modified with Ir and Pt: Synergistic Electrocatalysis between Structure and Composition

Active oxygen evolution reaction electrocatalysts for water splitting have received great attention because of their importance in the utilization of renewable energy sources. Here, the electrochemical oxygen evolution reaction activities of a nanoporous gold (NPG)‐based electrode in acidic media are investigated. The dependence of the oxygen evolution reaction activity on the NPG surface area shows that the large electrochemical surface areas of the NPG are effectively utilized to enhance electrocatalytic activity. The NPG surfaces are modified with Pt using atomic layer electrodeposition methods, and the resulting NPG@Pt exhibited enhanced electrocatalytic activities compared to those of the NPG and flat Pt electrodes. Ir‐modified NPG (NPG@Ir) electrodes are prepared by spontaneous exchange of Ir on NPG surfaces and exhibit enhanced electrocatalytic activity compared to that of flat Ir surfaces. The modification of NPG@Pt with Ir results in NPG@Pt/Ir electrodes, and their electrocatalytic activities exceed those of NPG@Ir. The enhanced oxygen evolution reaction activity on NPG@Pt/Ir over that on NPG@Ir surfaces is examined by X‐ray photoelectron spectroscopy. The oxygen evolution reaction activity on NPG@Pt/Ir surfaces demonstrates synergistic electrocatalysis between the nanoporous surface structure and active electrocatalytic components.     

Electrooxidation and Amperometric Detection of Ascorbic Acid at GC Electrode Modified by Electropolymerization of N,N‐Dimethylaniline

The polymer film of N,N‐dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N‐dimethylaniline (PDMA) film‐coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (?): 0.3±0.02 μm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl_(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film‐coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (D_s) were estimated by rotating disk electrode voltammetry: D=(5.5±0.1)×10^?6 cm² s^?1 and D_s=(6.3±0.2)×10^?8, (6.0±0.2)×10^?8 and (4.7±0.2)×10^?8 cm² s^?1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential‐step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 μM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 μA cm^?2 μM^?1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film‐coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice.     

Flow Injection Amperometric Detection at Enzyme‐Modified Gold Nanoelectrodes

Gold nanotubular electrode ensembles were prepared by using electroless deposition of the metal within the pores of polycarbonate particle track‐etched membranes. Glucose oxidase (Gox), used as a model enzyme, has been immobilized onto preformed self‐assembled monolayers (mercaptoethylamine or mercaptopropionic acid) on electroless gold via cross‐linking with glutaraldehyde or covalent attachment by carbodiimide coupling. Flow‐injection analysis systems in flow‐through or wall‐jet configurations using these Gox‐modified nanoelectrodes are described. The influence of different experimental parameters (i.e., applied potential, flow rate, interferents…?) on the analytical response of the sensor to glucose has been evaluated. Under optimized conditions, very reproducible results (standard deviations <4%, n=38) were obtained, linear calibration was achieved in the 2×10^?4 M to 3×10^?2 M concentration range and the detection limit was 2×10^?4 M. Moreover, no significant interferences from species like ascorbic and uric acids were observed at a potential of +0.9 V.     

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.     

葡萄糖氧化酶在纳米金修饰的丝网印刷电极上的直接电子传递及应用研究

制作了一次性使用的无介质丝网印刷传感器。研究了葡萄糖氧化酶在纳米金修饰的丝网印刷碳电极(GOD/Au/SPCE)上的电化学行为,在0.1mol/L和pH5.0的磷酸盐缓冲体系中,吸附在金胶纳米粒子上的葡萄糖氧化酶能保持其生物活性并催化溶解氧的还原,还原催化电流随葡萄糖溶液的加入而降低,线性范围为3.0×10-5～4.0×10-4mol·L-1,检出限为1.0×10-5mol·L-1。方法简便快速,可用于葡萄糖的测定。     

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.     

电流型电化学遥测系统的研制与应用

研制了一种微型嵌入式遥测系统,并利用此系统实现了电化学传感检测。遥测系统的输出电压范围为-0.5~0.5 V,分辨率<1 mV;电流检测范围为-1~1μA,最小分辨率为0.2 nA。此遥测系统是基于ADuCM360微处理器设计的,包括恒电位仪、电流检测模块和无线模块,尺寸大小为24 mm ×13 mm ×11 mm。利用LabVIEW开发上位机软件,用于数据存储和实时显示。为了验证该系统的精度和可靠性,对系统进行了电学性能测试。应用遥测系统检测不同浓度抗坏血酸溶液的电流响应,电极施加的工作电位为30 mV,在浓度范围50~300μmol/L 内,抗坏血酸电极的电流响应与其浓度呈现良好的线性关系,线性方程为I(nA)=2.98CAA(μmol/L)-137.39,线性相关系数R2=0.984。并以脑缺血模型为例,探索了仪器在活体动物研究中的适用性。结果表明,该系统可用于相关动物模型的研究。     

Anti‐Interferent Properties of Oxidized Nickel Based on Layered Double Hydroxide in Glucose Amperometric Biosensors

An amperometric biosensor based on Pt electrodes modified with a thin film of a Ni, Al layered double hydroxide (LDH), submitted to a preliminary oxidative treatment in order to have the nickel centers at the oxidation state +4, and glucose oxidase (GOx) is presented. The oxidized LDH acts both as a system to support the enzyme and as a barrier to anions since it acquires an overall negative charge, as demonstrated by electrochemical impedance spectroscopy. Even if the biosensor response is due to the detection of H₂O₂ at anodic potentials, glucose can be accurately determined in the presence of ascorbic acid or other interferences, commonly present in real matrices in anionic form, since they can not reach the electrode surface. The effectiveness of the developed biosensor has been demonstrated by measuring glucose in samples of fruit juices containing ascorbic acid at high levels.     

Amperometric Determination of Ascorbic Acid at an Electrodeposited Redox Polymer Film Modified Gold Electrode

A sensitive and selective electrochemical method for the determination of ascorbic acid was developed. It was shown that a hydrated osmium complex‐containing redox polymer film can be electrodeposited at the gold electrode and it exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid. In contrast to a bare gold electrode, the oxidation current of ascorbic acid increased greatly and the oxidation peak potential shifted negatively to about 0.01 V (vs. SCE) at the modified electrode. Amperometric measurements were performed at an applied potential of 0.01 V and a linear response was obtained in the range of 2–400 μM with a limit of detection (LOD) of 0.6 μM (S/N=3). The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of uric acid and dopamine. The proposed procedure was successfully applied to the determination of ascorbic acid in human urine samples.     

Highly Selective and Sensitive Amperometric Biosensing of Glucose at Ruthenium-Dispersed Carbon Paste Enzyme Electrodes

Abstract

The selectivity and sensitivity of glucose measurements at carbon-paste based amperometric biosensors are greatly enhanced through the use of ruthenium-dispersed graphite particles. The improved performance is attributed to the substantial lowering of the overvoltage for the reduction of the hydrogen peroxide product. Hence, cathodic measurements of glucose can be caried out at an optimal potential range (-0.15 to +0.20 V). Contributions from easily oxidizable substances (e.g. acetaminophen, ascorbic and uric acids) are eliminated, without the need for mediators or membrane barriers. The electrocatalytic action of the ruthenium sites results also in a substantially improved sensitivity. A fast flow injection operation is illustrated.     

Application of a Square‐Wave Potential Program for Time‐Dependent Amperometric Detection in Capillary Electrophoresis

Use of a square‐wave potential program for time‐dependent amperometric detection of analyte zones in capillary electrophoresis (CE) is described. Electrochemical detection for CE requires that the separation field be isolated from that of the electrochemical detection. This is generally done by physically separating the CE separation field from that of the detection. By applying a time variant potential program to the detection electrode, the detector current has a time dependence that can be used to help isolate the electrochemical detection current from that of the separation. When using a 20 μm inner‐diameter capillary, we find that a square‐wave potential program decreases the RMS baseline current from 4.5×10^?10 A, found with a constant potential amperometric detection, to 1.1×10^?10 A when using a square‐wave potential program. With a 75 μm inner‐diameter capillary, the improvement is even more dramatic, from 2.3×10^?9 A with amperometric detection to 2.06×10^?10 A when using a 1 Hz square‐wave potential program. When not using the time‐dependent detection with the 75 μm capillary, the analyte zones were beneath the S/N for the system and not detected. With the square‐wave potential program and time‐dependent detection, however, the analyte zones for an electrokinetic injection of 200 μM solution of 2,3‐dihydroxybenzoic acid were observed with the 75 μm inner‐diameter capillary. The improvement in the ability to discriminate the analytical signal from the background found experimentally is consistent with modeling studies.     

Gold Nanoparticles Modified Titania Nanotube Arrays for Amperometric Determination of Ascorbic Acid

Development and use of highly ordered, vertically aligned TiO₂ nanotube arrays modified with gold nanoparticles for the selective detection of ascorbic acid (AA) in the presence of uric acid and glucose are reported here. Gold nanoparticles were electrodeposited on the Nanotube arrays by CV. The sensor was characterized using SEM, EDS, CV, and EIS. It showed very good performance with a sensitivity of 46.8 μA mM^?1 cm^?2, response time below 2 seconds and linearity in the range of 1 μM to 5 mM with a detection limit of 0.1 μM and was tested for the AA concentration in pharmaceutical preparations.     

Nonenzymatic Glucose Detection with Good Selectivity Against Ascorbic Acid on a Highly Porous Gold Electrode Subjected to Amalgamation Treatment

A nonenzymatic glucose sensor with good selectivity for the ascorbic acid oxidation is presented. After the gold polycrystalline electrode was subjected to amalgamation treatment, two advantageous effects were observed. One is the enhancement of the surface roughness and the other is an increase in the catalytic current in the glucose oxidation. Besides the known first effect, the latter provided another advantageous effect in a fabrication of nonenzymatic glucose sensor. Using a gold electrode subjected to amalgamation treatment for 60 s, two calibration curves for glucose oxidation at two different potentials of ?0.1 V and 0.25 V were obtained and compared. At the potential of ?0.1 V, at which no ascorbic acid was oxidized and no interference effect was observed, a current sensitivity of 16 μA cm^?2 mM^?1 from zero to 10 mM glucose concentration range was obtained. At the other potential of 0.25 V, at which ascorbic acid was easily oxidized, a satisfactory calibration curve with negligible ascorbic acid interference was also obtained together with a more enhanced current sensitivity of 32 μA cm^?2 mM^?1.     

Electrochemical Fabrication of Cobalt Oxides/Nanoporous Gold Composite Electrode and its Nonenzymatic Glucose Sensing Performance

A nonenzymatic glucose sensor was successfully established by electrochemically decorating cobalt oxides (CoO_x) on a nanoporous gold electrode (NPG) using cobalt hexacyanoferrate (CoHCF) as a precursor. It exhibited high sensitivity and long‐term stability as well as satisfactory quantification of glucose concentration in human serum samples. The morphology and surface analysis of the resulting CoO_x/NPG were carefully characterized. Two detection methods, cyclic voltammetry and amperometry, were employed to evaluate the performance of CoO_x/NPG towards glucose sensing in alkaline solution. Using cyclic voltammetry, at ?0.5 V, the glucose partial oxidation peak current is linear to the glucose concentration up to 14 mM with a sensitivity of 283.7 µA mM^?1 cm^?2. A linear amperometric response at 0.55 V was obtained in the glucose concentration range from 2 µM to 2 mM with a sensitivity of 2025 µA mM^?1 cm^?2 and a response time <3 s.     

离子色谱中的安培检测方法及其应用

介绍了离子色谱中的安培检测方法(包括恒电位安培检测法、脉冲安培检测法和积分脉冲安培检测法)的原理和应用。脉冲安培检测法与高效阴离子交换色谱结合(HPAEC-PAD)是一种新的分析糖类化合物的方法;积分脉冲安培检测法与高效阴离子交换色谱结合(HPAEC-IPAD)是一种新的氨基酸分析方法。     

Separation and Detection of Nitrophenols at Capillary Electrophoresis Microchips with Amperometric Detection

A miniaturized analytical system for the separation and amperometric detection of toxic nitrophenols, based on the coupling of a micromachined capillary electrophoresis (CE) chip with a glassy carbon detector is described. This microsystem enables a rapid (120 s/sample) simultaneous determination of five priority nitrophenolic pollutants (2‐nitrophenol, 3‐nitrophenol, 4‐nitrophenol, 2,4‐dinitrophenol, and 2‐methyl‐4,6‐dinitrophenol). These compounds can be detected down to the 1×10^?5 M level using a 15 mM phosphate buffer pH 7.2 (containing 1.3 mM α‐cyclodextrin) as running solution on 77 mm long microchannel by applying a separation voltage of 3000 V and a negative potential of ?0.7 V (vs. Ag /AgCl wire). Applicability to ground water samples was demonstrated.     

Electrocatalytic Determination of Ascorbic Acid Using a Palladium Coated Nanoporous Gold Film Electrode

Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of ascorbic acid (AA) on palladium coated nanoporous gold film (PdNPGF) electrode. The deposition of palladium was done through oxidation of copper UPD layer by palladium ions. This low Pd‐loading electrode behaved as the nanostructured Pd for electrocatalytic reaction. The PdNPGF electrode exhibits excellent electrocatalytic behavior by enhancing the AA oxidation peak current due to synergistic influence of the Pd film and NPGF. The kinetic parameters such as electron transfer coefficient, α, was 0.47 and the voltammetric responses of the PdNPGF electrode were linear against concentration of AA in the ranges of 2.50–33.75 mM and 0.10–0.50 mM with CV and DPV respectively.     

Electrooxidation of Aliphatic and Aromatic Amines at a Ni,Al Based Hydrotalcite Modified Electrode

The electrocatalytic oxidation of a wide series of aliphatic and aromatic amines was investigated in alkaline solutions at a gold electrode modified with a Ni,Al based hydrotalcite. All the amino compounds, with the exception of pyridine, were detected by the amperometric sensor. Chronoamperometric measurements at a rotating disk allowed us to use the same modified electrode for sequential analysis of several analytes in order to investigate the factors affecting the electrochemical response. By varying the characteristics of the substrate, parameters like steric hindrance, kind of amino group, and number of oxidizable sites have been studied. The concentration ranges, where the amperometric response was linear, have been determined for the amines investigated.     

Congo Red Immobilized on a Silica/Aniline Xerogel: Preparation and Application as an Amperometric Sensor for Ascorbic Acid

Congo red (CR) was immobilized on a silica/aniline xerogel through electrostatic interaction. The dye is strongly retained and is not easily leached from the xerogel matrix. The material containing the adsorbed dye was used to prepare a carbon paste electrode and the electrochemical properties of the hybrid material were investigated using cyclic voltammetry and amperometry. The modified electrode was used to study the electrochemical oxidation of ascorbic acid. The adsorbed dye mediates ascorbic acid oxidation at the solid electrode surface‐solution interface at an anodic potential of 0.18 V at pH 7, in a 0.5 mol L^?1 KCl solution. This novel modified carbon paste electrode shows good analytical performance for the determination of ascorbic acid in commercial Vitamin C tablets.