Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution

Gold nanoparticles (Au‐NPs), cystamine (CA) and 3,3′‐dithiodipropionic acid (DTDPA) modified gold bare electrodes were applied in voltammetric sensors for simultaneous detection of norepinephrine (NEP), ascorbic (AA) and uric (UA) acids. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 μM to 600 μM M with the detection limit ≤0.091 μM for the electrodes modified at 2D template and in the range of 0.1 μM to 700 μM M with the detection limit ≤0.087 μM for the electrodes modified at 3D template The results have shown that using modified electrodes it is possible to perform electrochemical analysis of norepinephrine without interference of ascorbic and uric acids, whose presence is the major limitation in norepinephrine determination at a bare gold electrode. The modified SAMs electrodes show good selectivity, sensitivity, reproducibility and high stability.     

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution. Part II

Gold electrodes modified with S‐containing compounds and gold were used for determination of norepinephrine (NEP) in aqueous solution. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 µM to 600 µM with the detection limit ≤0.090 µM for the electrodes modified at 2D template and in the range of 0.1 µM to 700 µM with the detection limit ≤0.075 µM for the electrodes modified at 3D template. The results have shown that modified electrodes could clearly resolve the oxidation peaks of norepinephrine, ascorbic (AA) and uric acid (UA) with peak‐to‐peak separation enabling determination of NEP, AA and UA in the presence of each other.     

Electrochemical Formation of Nanostructured Gold Surfaces on Glassy Carbon for the Determination of Dopamine

Nanostructured gold surfaces were prepared by potentiostatic, potentiodynamic or galvanostatic Au electrodeposition on glassy carbon electrodes. The nanostructured gold electrodes (nsAu/GC) were used for the determination of dopamine (DA) in aqueous media. A directly proportional relationship was found between the peak current for DA (obtained by square wave voltammetry, SWV) and its concentration for all cases. However, the best performance for DA determination was attained with potentiodynamically electrodeposited surfaces. The SWV peak current was linearly dependent on DA concentration up to 10 μM, with a detection limit (3σ) of 0.57 μM, and a correlation coefficient (r) of 0.9966. A study on the effect of common interfering species such as ascorbic acid (AA) and uric acid (UA) on DA determination was also carried out. The use of a nanostructured surface gives rise to peaks for AA and UA that appear at 0.15–0.20 V above the peak potential for DA. The detection limit obtained for dopamine is below 1 μM in the presence of 0.1 mM AA and 0.1 mM UA. Thus, nanostructuring of glassy carbon surfaces with gold conveniently and easily improves the detection of DA in the presence of their principal interfering species.     

Electrocatalytic Application of an Overoxidized Dopamine Film Prepared on a Gold Electrode Surface to Selective Epinephrine Sensing

A dopamine polymer film was prepared ex situ on a bare gold template from a 10 mM dopamine solution in phosphate buffer, pH 7 followed by an overoxidation in 500 mM NaOH. The modified electrode was used for quantitative determination of epinephrine. A linear relationship between epinephrine concentration and current response was obtained in the range between 2 μM and 800 μM with the detection limit of 0.3 μM. The results have shown that using the overoxidized dopamine film it is possible to perform electrochemical analysis of epinephrine without interference of ascorbic and uric acids.     

Gold Microelectrodes Decorated by Spike-Like Nanostructures as a Promising Non-Enzymatic Glucose Sensor

Gold microelectrodes modified via easy method by gold nanostructures were studied as an ideal substrate for non-enzymatic glucose detection. The results confirmed that spike-like nanostructure displays the best electrocatalytic activity because of higher amount of edges. Results prove that modified electrode is able to detect glucose in two linear ranges from 100–500 μM and 0.5–30 mM, with limit of detection (48 μM), high sensitivities for both linear ranges (1.7 μA/mM and 2.4 μA/mM), and good stability. In addition, modified electrodes were able to detect glucose in blood serum. This work demonstrates glucose detection on miniaturised system.     

Gold-dendrimer Nanocomposite Based Electrochemical Sensor for Dopamine

An electrochemical sensor for dopamine was developed by electrodepositing poly(propylene imine) (PPI) dendrimer and gold nanoparticles (AuNPs) onto a glassy carbon electrode (GCE). Electrochemical characterisation of the sensor was carried out by cyclic voltammetry and electrochemical impedance spectroscopy in ferri/ferrocyanide electrolyte. The nanocomposite electrode (GCE-PPI-AuNPs) showed improved electroactive surface area and electrochemical response over bare GCE. The sensor recorded a detection limit of 0.16 μM over a concentration range of 0.1 μM to 125 μM. The sensor was applied for dopamine detection in human serum samples and in the presence of interfering substances such as ascorbic acid and epinephrine.     

Composite Assembly of Silver Nanoparticles with Avidin and Biotinylated AChE on Gold for the Pesticidal Electrochemical Sensing

An amperometric pesticide biosensor has been devised by the composite assembly of silver nanoparticles with avidin and biotinylated acetylcholinesterase (AChE) on gold electrodes modified with a biotin‐terminated self assembly monolayer (SAM). This composite assembly strategy takes use of the biospecific recognition avidin with the biotin from the SAM‐terminals and biotinylated AChE, as well as the electrostatic interaction between silver nanoparticles with negatively charged citrate shell and avidin with encounter charge at pH 7.2. The construction process of the composite interface on gold was monitored by surface plasmon resonance (SPR), and its structure was characterized by attenuated total reflection Fourier‐transform infrared spectra, atomic force microscopy and UV‐vis spectra. The composite interface shows excellent electron transfer ability, as characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimum conditions a quantitative measurement of organophosphate pesticide dimethoate was achieved with the linear range of 0.05 μM to10 μM and the detection limit 0.01 μM, taken as the concentration equivalent to a 10% decrease in signal. Silver nanoparticles conjugated biotin‐avidin system represents a simple and functional approach to the integration of electrode sensing interface with improved biocompatibility and electron transfer ability, which may provide an analytical access to a large group of enzymes for bioelectrochemical application.     

Diamond Electrodes for High Sensitivity Mercury Detection in the Aquatic Environment: Influence of Surface Preparation and Gold Nanoparticle Activity

This work compares polished and unpolished boron doped diamond (BDD) electrodes decorated with two sizes of gold nanoparticles (AuNPs) for use as robust mercury sensors in aquatic environments. The size of the catalytically active AuNPs on the electrode surfaces was demonstrated to have a less significant effect on the sensitivity for mercury detection than the surface preparation of the BDD. The lowest limits of detection were achieved with the polished BDD electrodes, which both detected mercury at a concentration of 1 pM, six orders of magnitude greater sensitivity than the lowest detection limit of 5 μM achieved with an unpolished BDD electrode, and high in comparison with other reported electrode systems.     

EQCM and Fluoroelectrochemical Studies on the Catalytic Oxidation of NADH at a Pencil 8B‐Scrawled Gold Electrode with High Detection Sensitivity

We report for the first time the effective catalytic electrooxidation of nicotinamide adenine dinucleotide (NADH) on the pencil 8B‐scrawled gold electrode of an electrochemical quartz crystal microbalance (EQCM). The EQCM allowed us to quantitatively evaluate the catalytic activity of the pencil‐scrawled Au electrode. With increasing the mass of modified pencil powders, the peak potential for NADH oxidation shifted negatively, with maximum shift of ?0.35 V at saturated pencil modification; the NADH‐oxidation peak current density (j_p) was also notably increased, and the j_p at saturated pencil modification was found to be larger than those at conventional pencil 8B and bare Au electrodes. Sensitive amperometric detection of NADH was achieved at the gold electrode with saturated pencil modification, with low detection potential (0.4 V versus SCE), low detection limit (0.08 μmol L^?1) and wide linear range (0.2–710 μmol L^?1). The fluoroelectrochemical measurements of NADH at bare and pencil‐modified gold electrodes were also conducted with satisfactory results. The convenient and low‐cost modification of pencil powders on the Au electrode may have presented a new functional surface of the EQCM, which is recommended for wider applications to bioelectrochemical studies, especially in view of the EQCM's capability of providing abundant in situ information in relevant processes.     

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.     

Amplified Electrochemical DNA Sensor Based on Polyaniline Film and Gold Nanoparticles

In this work, an electrochemical DNA biosensor, based on a dual signal amplified strategy by employing a polyaniline film and gold nanoparticles as a sensor platform and enzyme‐linked as a label, for sensitive detection is presented. Firstly, polyaniline film and gold nanoparticles were progressively grown on graphite screen‐printed electrode surface via electropolymerization and electrochemical deposition, respectively. The sensor was characterized by scanning electron microscopy (SEM), cyclic voltammetry and impedance measurements. The polyaniline‐gold nanocomposite modified electrodes were firstly modified with a mixed monolayer of a 17‐mer thiol‐tethered DNA probe and a spacer thiol, 6‐mercapto‐1‐hexanol (MCH). An enzyme‐amplified detection scheme, based on the coupling of a streptavidin‐alkaline phosphatase conjugate and biotinylated target sequences was then applied. The enzyme catalyzed the hydrolysis of the electroinactive α‐naphthyl phosphate to α‐naphthol; this product is electroactive and has been detected by means of differential pulse voltammetry. In this way, the sensor coupled the unique electrical properties of polyaniline and gold nanoparticles (high surface area, fast heterogeneous electron transfer, chemical stability, and ease of miniaturisation) and enzymatic amplification. A linear response was obtained over a concentration range (0.2–10 nM). A detection limit of 0.1 nM was achieved.     

Selective and Simultaneous Determination of Dihydroxybenzene Isomers Based on Green Synthesized Gold Nanoparticles Decorated Reduced Graphene Oxide

In the present study, we report the simultaneous electrochemical determination of hydroquinone (HQ), catechol (CC) and resorcinol (RC) at gold nanoparticles (Au‐NPs) decorated reduced graphene oxide (RGO) modified electrode. An enhanced and well defined peak current response with a better peak separation of HQ, CC and RC is observed at RGO/Au‐NPs composite than that of RGO and Au‐NPs modified electrodes. The fabricated modified electrode shows a wide linear response in the concentration range of 3–90 µM, 3–300 µM and 15–150 µM for HQ, CC and RC, respectively. The detection limit of HQ, CC and RC is found as 0.15 µM, 0.12 µM and 0.78 µM, respectively.     

Graphene sheet for improving the electrocatalytic activity of a benzofuran derivative modified electrode for determination of epinephrine in the presence of serotonin

A nanocomposite system based on coumarin derivative and graphene sheet was used to prepare a new electrochemical sensor. The objective of the mentioned nanocomposite was to investigate novel electrochemical properties enabling the quantification of epinephrine (Ep). Cyclic voltammetry was used to study the redox properties of the mentioned modified electrode at different scan rates. Henceforward, the electrocatalytic oxidation of Ep at the surface of the modified electrode was considered. The data has shown excellent catalytic activity of the modified electrode for the electrooxidation of Ep, which leads to a reduction of overpotential for more than 238 mV. According to differential pulse voltammetry (DPV), the oxidation of Ep showed a dynamic range between 0.1 and 1000.0 μM and the detection limit (3s) of 0.011 μM. Besides, DPV was used for the determination of Ep at the mentioned modified electrode in the presence of serotonin.     

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.     

电还原氧化石墨烯-金纳米棒修饰电极对酒石黄的测定

本文制备了氧化石墨烯-金纳米棒复合物(GO-GNRs).利用滴涂法制备了修饰电极(GO-GNRs/GCE),通过循环伏安法,还原了GO-GNRs复合物中的GO,制得电化学还原的石墨烯-金纳米棒修饰电极(ERGO-GNRs/GCE).研究了酒石黄在不同电极上的电流响应,结果表明,ERGO-GNRs/GCE对酒石黄的氧化有很好的电催化作用,其浓度在0.05～6.0μmol/L范围内与氧化峰电流呈良好的线性关系,检出限为15 nmol/L.利用ERGO-GNRs/GCE可完成样品中酒石黄含量的测定.     

Determination of Copper in the Presence of Various Amounts of Arsenic with L‐Cysteine Modified Gold Electrodes

An L ‐cysteine modified gold electrode for the determination of copper in the presence of various amounts of arsenic with anodic stripping voltammetry has been studied. The electrode was fabricated by immersing a gold electrode in an ethanol solution of 5mM L ‐cysteine for 60 min. Various parameters, such as the effect of different supporting electrolytes, the pH of the electrolyte and the deposition potential were investigated. Under optimum conditions, copper was accumulated at ?0.3 V (vs. SEC) for 60 s in 0.1 M phosphate buffer pH 5.0 in the presence of different amounts of arsenic. Essentially the same sensitivities (0.33±0.001 μA/μM) and limits of detection (0.13±0.002 μM) of copper were obtained with various amount of arsenic in the range 2 μM to 20 μM.     

Highly Selective Nanostructured Electrochemical Sensor Utilizing Densely Packed Ultrathin Gold Nanowires Film

The number of studies conducted about nonenzymatic electrochemical sensors has increased in recent years due to the development of more stable and robust electrodes using noble metals. One of the key aspects for achieving high sensing performance including detection limit and sensitivity is the design of electrode architecture. Herein, we report a new electrochemical sensing platform featuring ultrathin standing gold nanowires (AuNWs) for nonenzymatic detection of hydrogen peroxide (H₂O₂). The use of AuNWs resulted in an increased electron transfer efficiency due to the higher active surface area compared to traditional gold film electrodes. This sensor demonstrates good selectivity, reproducibility, a linear range up to 49.5 mM of H₂O₂ with a sensitivity of 0.185±0.003 mAmM^?1cm^?2 and a limit of detection of 111 μM. The biological relevance of this sensor was tested in cell culture media to illustrate the performance of the proposed sensing electrode in complex biological media.     

Comparison of biosensors based on gold and nanocomposite electrodes for monitoring of malic acid in wine

Amperometric biosensors based on a gold planar electrode and on two types of nanocomposite electrodes consisting of multi-walled carbon nanotubes for the determination of L-malic acid designed for wine-makers were developed. The biosensors designed for wine-makers were constructed by immobilization of L-malate dehydrogenase and diaphorase within chitosan layers on the surface of the electrodes. The coenzyme NAD+ and the electrochemical mediator ferricyanide were present in the measuring solution. The current resulting from re-oxidation of produced ferrocyanide was measured at a working potential of +300 mV against an Ag/AgCl reference electrode. The biosensor based on a gold electrode showed linearity over the range 10–520 μM with a detection limit of 5.41 μM. Calibration curves for biosensors utilizing nanocomposites were obtained both with the linear range of 10 to 610 μM. The detection limits were 1.57 and 1.77 μM, respectively. The biosensors showed satisfactory operational stability (no loss of sensitivity after 30 consecutive measurements) and storage stability (90% of the initial sensitivity after one year of storage at room temperature). The results obtained from measurements of wine samples were in a good correlation with the standard HPLC method. Satisfactory biosensor sensitivity, specificity and stability allowed their successful commercialization.     

Gold Surface Functionalization with S‐containing Organic Compounds and Gold Nanoparticles for Ethylene Glycol Electrooxidation

In this work a gold electrode modified with self‐assembled layers (SAMs) composed with organic S‐containing compound and gold nanoparticles was prepared. The electrode with SAMs endowed with gold nanoparticles gave the high catalytic effect for ethylene glycol (EG) electrooxidation in solution at pH 7. For this novel sensor a linear relationship between the current response of EG at the potential of peak maximum (j_p) and the concentration of this compound in solution (c_EG) was found over the range 0.1 µM to 0.7 M with the detection sensitivity j_p/c_EG equal to about 5 A cm^?2 mol^?1 dm³ (at v=0.1 V s^?1) and the detection limit of 0.046 µM.     

Flufenamic Acid Determination in Human Serum by Adsorptive Voltammetry with In Situ Surfactant Modified Carbon Paste Electrodes

A simple and sensitive adsorptive- differential pulse- voltammetric method for the determination of flufenamic acid (FFA) is presented. The method is based on the preconcentration of FFA on carbon paste electrodes modified in situ with cationic surfactants, dodecyltrimethylammonium chloride (DTAC) or cetyltrimethylammonium chloride (CTAC), at submicellar concentrations. The best results were obtained with DTAC-modified electrodes. After optimization, with these electrodes and using an accumulation step at 0 V for 3 minutes in 0.1 M phosphate solutions pH 7, the peak current of the main oxidation process of FFA varies linearly with its concentration from 1×10⁻⁹ M to 5×10⁻⁵ M, with a limit of detection of 0.64 nM (0.2 ng/mL). The proposed method has been applied to the determination of FFA in spiked serum samples, treated with acetonitrile to separate the proteins. In the concentration range studied (3 μM to 65 μM) the recovery was near 100 % and the lowest concentration attainable in these samples is below 3 μM (0.8 ppm).