Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH

Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for β-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.     

Reduced graphene sheets modified glassy carbon electrode for electrocatalytic oxidation of hydrazine in alkaline media

This paper describes the electrochemical properties of reduced graphene sheets (RGSs) for the electrocatalytic properties towards the hydrazine oxidation in alkaline media. The RGSs have been produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. The RGSs possess excellent electrocatalytic activity towards the hydrazine oxidation. In our opinion, RGSs are a potential electrode material for direct hydrazine fuel cells and electrochemical sensors for hydrazine detection.     

Electroanalytical Approach for Quantification of Pesticide Maneb

For the first time, in this study electrochemical oxidation behavior of pesticide maneb is evaluated. Due to the structure electroanalytical quantification of maneb has not been exploited enough. Maneb electrochemical behavior was investigated using glassy carbon (GC), graphene modified glassy carbon (GR/GC) and boron doped diamond (BDD) electrodes. It is shown that only BDD shows satisfactory results toward maneb detection. Based on this, a simple, sensitive and selective electroanalytical method for determination of pesticide maneb using differential pulse voltammetry (DPV) is proposed, with a working linear range of 80–3000 nM and the limit of detection of 24 nM. The developed methodology has been applied for the determination of maneb in river water samples with satisfactory recovery. Additionally, this green method, being simple, fast, and free of chemical‐reduction reagents, offers several advantages over modified electrodes and expands the scope of BDD based electrochemical sensing devices, with promise for wider applications in environmental analysis.     

Lead Sulfide Nanoparticle as Oligonucleotides Labels for Electrochemical Stripping Detection of DNA Hybridization

We report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. A kind of lead sulfide nanoparticle with free carboxyl groups on its surface was synthesized in aqueous solution. The nanoparticle was used as a marker to label a sequence‐known oligonucleotide, which was then employed as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were monitored by the oxidation dissolution of the lead sulfide anchored on the hybrids and the indirect determination of the lead ions by anodic stripping voltammetry (ASV). The detection limit is 0.3 pmol L^?1 of target oligonucleotides. The PbS nanoparticle combining its easy conjugation to the DNA molecule with the highly sensitive stripping voltammetry detection of lead shows its promising application in the electrochemical DNA hybridization analysis assay.     

Electrochemical sensing of gases based on liquid collection interfaces

Although many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.     

Increased electrochemical detector sensitivity by electrode surface modification

Summary Electrode surface modification by electrochemical pretreatment of glassy carbon electrodes was shown to enhance significantly the sensitivity of the electrodes for the detection of timolol and oxprenolol, but reduce slightly the sensitivity to prenalterol. This method may permit the detection of exprenolol and timolol with increased sensitivity, or may allow their detection at lower applied potentials than is presently possible. Electrode surface modification may prove to be a valuable aid to the detection of compounds that are considered to be outside the practical limits of electrochemical detection.     

聚萘二胺修饰电极对痕量物质的检测

综述了聚萘二胺修饰铂电极、玻碳电极和碳糊电极用于检测痕量银离子、铅离子、亚硝酸根及硝酸根阴离子、过氧化氢、葡萄糖和胆甾醇等方面的研究成果，列举了这些电极的优异探测性能，并指出该类电极有望发展成为性能优异的检测电极和传感器。引用文献14篇。     

Electrochemical Investigation of Metal Oxide Conducting Electrodes for Direct Detection of Sulfide

This study examined the performance of four conducting metal oxide electrodes for the direct electrochemical analysis of sulfide; the electrode materials studied were indium tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum doped zinc oxide (AZO) and gallium doped zinc oxide (GZO). Cyclic voltammetry (CV) results obtained using the ITO, AZO, GZO and FTO electrodes showed direct electrooxidation peak potential of sulfide at 381, 507, 400, and 850 mV vs. Ag/AgCl, respectively; however, the less positive oxidation potential and high catalytic current response of the ITO electrode made it the electrode of choice for the direct oxidation of sulfide. The effects of different electrolytes and buffer solutions on the CV responses were also evaluated. A linear concentration range up to 350 µM and a detection limit of 8.0 µM were achieved. CV response was highly reproducible, remaining unaffected even after 50 measurements. The sensor was found to have good selectivity, with no interference from sulfite, sulfate or chloride ions. The present findings demonstrate that the bare ITO electrode can be used as the basis of an inexpensive, sensitive, selective and robust sulfide sensor.     

Electrochemical Sensor for Arabinose Based on Template‐free Pb/Cd Branched Nanorods on Glassy Carbon Electrode

In this paper, the electrochemical behavior of glassy carbon electrodes modified with Cd/Pb (GC/Cd/Pb) branched nanorodes (NRs) was studied using cyclic voltammetry technique. The obtained results showed that the branched nanorods of Cd/Pb can be readily prepared without any templates. The modified electrode was characterized using scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDAX) and electrochemical impedance spectroscopy (EIS) techniques. The electrocatalytic behavior of GC/Cd/Pb electrode showed an increase in oxidation signal of arabinose by increasing its concentration. The catalytic current was linearly related to arabinose concentration in the range of 0.6 to 6.8 μM with a limit of detection 0.2 μM.     

Effect of Various Deposition Techniques,Electrode Materials and Posttreatment with Tetrabutylammonium and Tetrabutylphosphonium Salts on the Electrochemical Behavior and Stability of Various Prussian Blue Modified Electrodes

The effect of various deposition techniques, electrode materials and posttreatment with tetrabutylammonium and tetrabutylphosphonium salts on the electrochemical behavior and stability of various Prussian blue (PB) modified electrodes, namely PB modified glassy carbon electrodes, silicate‐film supported PB modified glassy carbon electrodes, PB‐doped silicate glassy carbon electrodes, PB modified carbon ceramic electrodes using electrochemical deposition and PB modified carbon ceramic electrodes using chemical deposition is reported. Cyclic voltammetry and amperometric measurements of hydrogen peroxide were performed in a flow injection system while the carrier phosphate buffer (pH 7.0) with a flow rate of 0.8 mL min^?1 was propelled into the electrochemical flow through cell housing the PB modified working electrode as well as an Ag|AgCl|0.1 M KCl reference and a Pt auxiliary electrode. The results showed that the deposition procedure, electrode material and posttreatment with additional chemicals can significantly alter the stability and electrochemical behavior of the PB film. Among the studied PB modified electrodes, those based on carbon ceramic electrodes modified with a film of electropolymerized PB showed the best electrochemical stability.     

Electrochemical Glutathione Sensor Based on Electrochemically Deposited Poly‐m‐aminophenol

Preparation and characterization of electrodes suitable for determination of glutathione is reported in this study. For this poly‐m‐aminophenol (PmAP), poly‐o‐aminophenol, and poly‐p‐aminophenol were electrochemically deposited from aqueous solution on the surface of glassy carbon (GC) electrode by potential cycling in the range of +0.2–+1.0 V. The modified GC electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, contact angle measurement and ellipsometry. It was found that poly‐m‐aminophenol modified GC electrode (PmAP/GC‐electrode) is most suitable for electroanalytical determination of glutathione. An electroanalytical system for the determination of glutathione based on the PmAP/GC‐electrode was developed. The analytical system was characterized by low limit of detection, good stability, high sensitivity and wide linear detection range.     

Sensitive Electrochemical Detection of Bisphenol A Using Molybdenum Disulfide/Au Nanorod Composites Modified Glassy Carbon Electrode

Bisphenol A, an important compound that is classified as an environmental hormone, has been proven to have harmful effects on human health and ecology. A molybdenum disulfide/Au nanorod‐modified glassy carbon electrode was prepared as an electrochemical sensor for the detection of bisphenol A using a simple and convenient approach. UV–Vis spectrophotometry and transmission electron microscopy were employed to characterize the composite. The electrochemical behavior of bisphenol A at the modified electrode was investigated via differential pulse voltammetry and cyclic voltammetry. The results show that bisphenol A exhibits a good electrochemical signal at the modified electrode under optimized conditions, and a good linear relationship was observed between the bisphenol A concentration and peak current within the range of 0.01–50 μM, with a detection limit of 3.4 nM. Furthermore, the fabricated electrodes showed good anti‐interference, reproducibility and stability. The proposed electrochemical method was successfully applied for the detection of bisphenol A in milk and water samples, and its potential for applications in pollutant detection was demonstrated.     

Electrochemical detection of thrombin by sandwich approach using antibody and aptamer

The goal of this work was to introduce a modified electrochemical sandwich model for target protein detection, exploiting antibody as the capturing probe, aptamer as the detection probe and methylene blue as the electrochemical active marker intercalating in the probing aptamer without previous labeling. With appropriate design of the sequence of the aptamer, the aptamer was successfully utilized instead of antibody for obtaining the electrochemical detection. A special immobilization interface consisting of nanogold-chitosan composite film was used to improve the conductivity and performance characteristics of the electrode. The capturing antibody was linked to the glassy carbon electrodes modified with composite film via a linker of glutaraldehyde. Differential pulse voltammetry was performed to produce the response signal. Thrombin was taken as the model target analyte to demonstrate the feasibility of proposed methodology. The sensor shows the linear response for thrombin in the range 1-60 nM with a detection limit of 0.5 nM. The proposed approach provides an alternative approach for sandwich protein assay using aptamers.     

Using nanoparticle aggregation to give an ultrasensitive amperometric metal ion sensor

Herein we show an electrochemical sensor for the detection of copper ions that has a limit of detection below 1 pM. This extraordinarily low limit of detection is achieved in two ways. The first is to use SAM modified electrodes to give low background current where electron transfer to the underlying polycrystalline electrode is achieved through gold nanoparticles attached to the terminus of the SAM. The gold nanoparticles are modified with cysteine to allow copper accumulation. The second way the low detection limits are achieved is by the addition of cysteine-modified nanoparticles to the sample solution, as well as the SAM modified electrode. The complexation of copper with the nanoparticles in solution causes them to aggregate with these aggregates accumulating on the electrode. Thus a higher percentage of copper in the solution is collected at the electrode giving the enhanced detection limits.     

SNPs Feasibility of Nonlabeled Oligonucletides on Using Electrochemical Sensing

We have demonstrated an electrochemical gene chip protocol for the SNPs detection of nonlabeled DNA. Using an array consisting of streptavidin‐modified gold electrodes, probe DNA were attached through the application of a direct electric field. Electrochemical response changes originating from the hybridization of nucleic acids to protein‐bound nucleic acids using soluble mediators in K₃Fe(CN)₆ solution could then be observed. The electrochemical protocol developed showed high sensitivity and good reproducibility in the detection of DNA hybridization. Significant changes in electrochemical signals were also observed when using target DNA with a single base mismatch, indicating the applicability of this method to single nucleotide polymorphisms (SNPs) detection.     

Disposable Electrochemical Aptasensor for Ultrasensitive Determination of Aflatoxin B1 Using Copper Nanoparticles as Probes

An electrochemical aptasensor for aflatoxin B1 (AFB1) detection was constructed based on the copper nanoparticles (CuNPs) and gold nanoflowers modified screen-printed carbon electrodes as electrochemical probes and substrates, respectively. In the range of 100 aM to 100 pM, a good linear relationship between oxidation peak current of CuNPs and concentration of AFB1 was obtained. The high sensitivity could be ascribed to the amplified electrochemical signals by CuNPs. The high affinity of AFB1 with aptamer endowed its high selectivity. The above advantages and disposable traits made this aptasensor as an ideal platform for evaluation of AFB1 level in food samples.     

Development of an Amperometric Microbial Biosensor Based on Thiobacillus thioparus Cells for Sulfide and Its Application to Detection of Sulfate‐Reducing Bacteria

This paper describes a novel electrochemical microbial biosensor based on Thiobacillus thioparus cells for sulfide detection. The morphology and electrochemical properties of the proposed biosensor were characterized by SEM and cyclic voltammetry, respectively. Working conditions of the microbial biosensor were optimized to obtain good electrochemical performances. Under the optimum conditions, analytical performances were evaluated, and the results suggested that the microbial biosensor could be used for selective detection of sulfide. The microbial biosensor was then successfully applied in detection of sulfate‐reducing bacteria by oxidizing its characteristic metabolite, sulfide, which was accumulated in culture media during bacterial growth.     

3,4,9,10-Perylene Tetracarboxylic Acid Noncovalently Modified Multiwalled Carbon Nanotubes: Synthesis,Characterization, and Application for Electrochemical Determination of 2-Aminonaphthalene

Carbon nanotubes have been intensively studied for their diverse applications but are insoluble in water. In this paper, 3,4,9,10-perylene tetracarboxylic acid noncovalently modified multiwalled carbon nanotubes were prepared by a facile approach and applied successfully for electrochemical determination of 2-aminonaphthalene. Infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and electrochemical methods were used to characterize the hybridized nanotubes. The results reveal that the hybrids exhibit high dispersibility in water, and a glassy carbon electrode modified by the hybrids displayed a higher electrochemical response toward 2-aminonaphthalene than bare glassy carbon and multiwalled carbon nanotube–glassy carbon electrodes with a linear dynamic range of 15.0–500.0 nM and a detection limit of 4.5 nM. The modified hybrid electrode was successfully applied for the determination of 2-aminonaphthalene in water.     

Development of an Electrochemical Immunoassay Based on the Use of an Eight‐Electrodes Screen‐Printed Array Coupled with Magnetic Beads for the Detection of Antimicrobial Sulfonamides in Honey

In this work an electrochemical immunoassay, based on a direct competitive assay, was developed using magnetic beads as solid phase and carbon screen‐printed arrays as transducers for the detection of sulfonamides in food matrices such as honey. Magnetic beads coated with protein A were modified by immobilisation of specific antibodies and then the competition between the target analyte and the corresponding analyte‐labelled with an enzyme was carried out; after the immunosensing step, beads were captured by a magnet onto the working surfaces of a screen‐printed eight‐electrodes array for a multiple electrochemical detection. Screen‐printed eight‐electrodes arrays were chosen as transducers due to the possibility to repeat multiple analysis and to test different samples simultaneously. Alkaline Phosphatase (AP) was used as enzyme label and Differential Pulse Voltammetry (DPV) as fast electrochemical technique. Calibration curves demonstrate that the developed electrochemical immunoassay was able to detect this class of drugs in standard solutions at low concentrations (ng/mL levels). The short incubation times (25 min) and the fast electrochemical measurement (10 sec) make of these systems a possible alternative to classic ELISA tests.     

Graphene Nanocomposites Based Electrochemical Sensing Platform for Simultaneous Detection of Multi-drugs

Three reduced graphene oxide nanocomposites were employed to achieve the simultaneous electrochemical determination of multi-drugs including acetaminophen (ACTM), carbendazim (CB) and ciprofloxacin (CFX). All nanocomposite modified electrodes showed improved current responses for three drugs. Notably cauliflower-like platinum nanoparticles decorated reduced graphene oxide modified electrode (or Pt−RGO/GCE) exhibited the best performance in terms of electrochemical stability. Using Pt−RGO/GCE, the linear detect ranges of 30–120 μM, 25–115 μM and 10–25 μM, and detection limit values of 3.49, 2.96, and 1.53 μM were achieved for ACTM, CB and CFX respectively. The electrode was further used for the successful determination of above drugs in tap and river water using differential pulse voltammetry. From the obtained results, we believe that Pt-RGO/GCE is highly promising for the fabrication of robust electrochemical sensors for simultaneously determining ACTM, CB and CFX or similar types of drugs in the future.