Preparation of TEMPO‐Modified Electrodes by Electrochemical Polymerization in Aqueous Solution for Use in Electrochemical Analysis of Pharmaceuticals

Immobilization of Nafion-ordered mesoporous carbon on a glassy carbon electrode: Application to the detection of epinephrine

The bioelectrochemistry of the blue copper protein, pseudoazurin, at glassy carbon and platinum electrodes that were modified with single-wall carbon nanotubes (SWNTs) was investigated by multiple scan rate cyclic voltammetry. The protein showed reversible electrochemical behavior at both bare glassy carbon electrodes (GCEs) and SWNT-modified GCEs (SWNT|GCEs); however, direct electrochemistry was not observed at any of the platinum electrodes. The effect of the carbon nanotubes at the GCE was to amplify the current response 1000-fold (nA at bare GCE to µA at SWNT|GCE), increase the apparent diffusion coefficient D app of the solution-borne protein by three orders of magnitude, from 1.35 × 10−11 at bare GCE to 7.06 × 10−8 cm2 s-1 at SWNT|GCE, and increase the heterogeneous electron transfer rate constant k s threefold, from 1.7 × 10−2 cm s−1 at bare GCE to 5.3 × 10−2 cm s−1 at SWNT|GCE. Pseudoazurin was also found to spontaneously adsorb onto the nanotube-modified GCE surface. Well-resolved voltammograms indicating quasi-reversible faradaic responses were obtained for the adsorbed protein in phosphate buffer, with I pc and I pa values now greater than corresponding values for solution-borne pseudoazurin at SWNT|GCEs and with significantly reduced ΔE p values. The largest electron transfer rate constant of 1.7 × 10−1 cm s−1 was achieved with adsorbed pseudoazurin at the SWNT|GCE surface in deaerated buffer solution consistent with its presumed role in anaerobic respiration of some bacteria.

Electropolymerized molecular imprinting on gold nanoparticle-carbon nanotube modified electrode for electrochemical detection of triazophos

An electrochemical sensor for capsaicin based on two-dimensional titanium carbide (MXene)-doped titania-Nafion composite film

Simple and highly sensitive assay of axitinib in dosage form and biological samples and its electrochemical behavior on the boron-doped diamond and glassy carbon electrodes

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer‐by‐layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron‐transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long‐term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR‐modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite‐modified GC electrode is more than three‐fold greater than that of the MWNTs modified GC electrode, and nine‐fold greater than that of the PNR‐modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference‐free determination of glucose has been realized at −0.2 V vs. SCE with a linear range from 50 µM to 10 mM and response time <10s. The detection limit was 10 µM glucose (S/N=3).

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Electrocatalytic oxidation and selective determination of an opioid analgesic methadone in the presence of acetaminophen at a glassy carbon electrode modified with functionalized multi-walled carbon nanotubes: Application for human urine, saliva and pharmaceutical samples analysis

Electrochemical reduction behavior of Eu3+ on a multi-walled carbon nanotubes (MWCNTs)/sodium lauryl sulfate (SDS) (MWCNTs/SDS)-modified glassy carbon (GC) electrode was investigated by cyclic voltammetry (CV). Results indicated that the electrochemical reduction process of Eu3+ at the MWCNTs/SDS-modified GC electrode is a quasi-reversible and diffusion-controlled process. The value of standard rate constant (ks) at the MWCNTs/SDS-modified GC electrode was estimated to 1.96 × 10−2 cm s−1. CV studies showed that the electrochemical response of Eu3+ was directly related to the ratio of MWCNTs to SDS, and the tube diameter of MWCNTs had a slight influence on the electrochemical behavior of Eu3+, whereas the tube length. of MWCNTs had a strong influence. CVs results also proved that s-MWCNTs (with shorter tube length)-modified GC electrode showed better response to the electrochemical reaction of Eu3+.

Non-enzymatic electrocatalysts have recently received much attention as a glucose sensor. These catalysts basically contain transition metals such as Pt, Au, Ni, and Cu. The glucose adsorbs onto the surface of the catalytic electrode and is oxidized by hydroxyl radicals. Smaller structured materials make the surface area larger, thus nanostructured electrode is expected to show efficient oxidation of glucose. As a nanomaterial, nanosheets have recently received much attention as a new material with an ultimate two-dimensional anisotropy. Inorganic nanosheets have been prepared by delamination of layered materials. We synthesized copper hydroxide in which dodecylbenzene sulfonate intercalated and delamination of these compounds to monolayer nanosheets. Copper oxide and hydroxide are viable candidates for the non-enzymatic electrochemical glucose sensor, thus copper hydroxide nanosheets are expected to make novel non-enzymatic electrochemical glucose sensor. In this study, we synthesized copper hydroxide nanosheet and investigated its electrochemical oxidation of glucose. The precursor of the nanosheet was a layered copper hydroxide synthesized by the ion exchange of dodecylbenzene sulfonate with acetate in Cu2(OH)3(CH3COO)·H2O. The Cu2(OH)3(CH3COO)·H2O was synthesized by hydrolysis of Cu(CH3COO)2·H2O solution (0.1 M) by heating at 65 °C for several days until crystalline product formed. The Cu(OH)3(CH3COO)·H2O (0.042 g) was added to the solution of NaDBS (DBS– = dodecylbenzene sulfonate, 26.6 mM, 40 mL) and shaken at 30 °C for 18 h. The precipitate was separated by centrifugation and washed with water and air dried. The yielded product (0.053 g) is named as Cu-DBS. The nanosheet was prepared by delamination of Cu-DBS by dispersion in 1-butanol. To make dispersion, the Cu-DBS (0.03 g) in 1-butanol (45 mL) was shaken and let stand for 2-4 weeks. The supernatant of the dispersion was used to further measurements. To make a working electrode, the 15 g of the dispersion of the copper hydroxide nanosheet was concentrated by an evaporator and dried after dropped on the ϕ 3 mm glassy carbon (GC) electrode. Electrochemical measurements of this working electrode were carried out in a standard one-compartment cell equipped with an additional bare GC working electrode, a platinum wire counter electrode, and an Ag/AgCl reference electrode in 0.1 M NaOH solution. The morphology and size of nanosheets in the dispersion were examined by atomic force microscopy (AFM), which revealed nanosheet structure. The examined samples were prepared by deposition of a droplet of the dispersion on a silicon wafer. Intermittent contact mode AFM images showed two-dimensional ultrathin sheets with the lateral dimensions of ca. 2 μm. Some aggregates were occasionally observed. The height profile reveals that the sheets have a fairly flat terrace with a thickness of 4.33-6.30 nm with 320-460 aspect ratio and some sheets are stacked step by step with keeping the height. If DBS– ions place perpendicular to the hydroxide layer, the minimum thickness of the sheets should be ca. 5 nm because DBS– ions (22–25 Å) coordinate the hydroxide layer both on surfaces of the copper hydroxide sheet. Therefore DBS chains would align closely to the hydroxide layers at an angle of ca. 40 °. These copper hydroxide nanosheets are thin enough to be considered as a monolayer. Cyclic voltammetry (CV) was measured at 20 mV/s scan rate after addition of glucose solution to 0-2 mmol/l concentration (Fig. 1). The CV of the nanosheet coated electrode showed oxidation current peak at around +0.6 V vs. Ag/AgCl and this peak current increased as the concentration of glucose increased. This peak was not detected with only the GC electrode thus current peak was caused by the oxidation of glucose. Amperometry was measured at +0.6V vs. Ag/AgCl with successive addition of glucose solution (Fig. 2). The concentration of glucose increased to 0.1 to 27.8 mM, the current of the nanosheet coated electrode increased in a stepwise when glucose solution was added. The current was not detected with only the GC electrode. Glucose concentration and catalytic current were almost proportional. When the linear range is 0.1 to 4.9 mM, the sensitivity was 1.16 mA mM-1cm-2 from the slope. This value is comparable to the other glucose electrolytic oxidation electrodes using copper. Figure 1

Electrochemical sensor based on corncob biochar layer supported chitosan-MIPs for determination of dibutyl phthalate (DBP)

The surface of a glassy carbon (GC) electrode was modified with reduced graphene oxide (rGO) to evaluate the electrochemical response of the modified GC electrodes to hydrogen peroxide (H2O2) and hydrazine. The electrode potential of the GC electrode was repeatedly scanned from −1.5 to 0.6 V in an aqueous dispersion of graphene oxide (GO) to deposit rGO on the surface of the GC electrode. The surface morphology of the modified GC electrode was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM and AFM observations revealed that aggregated rGO was deposited on the GC electrode, forming a rather rough surface. The rGO-modified electrodes exhibited significantly higher responses in redox reactions of H2O2 as compared with the response of an unmodified GC electrode. In addition, the electrocatalytic activity of the rGO-modified electrode to hydrazine oxidation was also higher than that of the unmodified GC electrode. The response of the rGO-modified electrode was rationalized based on the higher catalytic activity of rGO to the redox reactions of H2O2 and hydrazine. The results suggest that rGO-modified electrodes are useful for constructing electrochemical sensors.

In this study, the electrochemical behaviour of Mordant dye (C.I. 17135) was investigated in Britton-Robinson (BR) buffer (pH 2.0-12.0) media by using different voltammetric techniques: square wave voltammetry (SWV), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and direct current voltammetry (DCV). The electrochemical behavior of the dye has been investigated by using a glassy carbon electrode (GCE) and silver electrode (SE). The brode peak of the azo dye occurred at SW and DP voltammograms, is due to its adsorption on the glassy carbon and silver electrode surfaces. Two reduction peaks were observed at pH &lt; 9.5, and one reduction peak was observed at pH &gt; 9.5 for SWV and DPV techniques at a glassy carbon electrode. From the voltammetric data electrochemical reaction mechanism of the azo dye has been suggested at glassy carbon and silver electrodes.

Highly sensitive electrochemical capsaicin sensor based on graphene-titania-Nafion composite film

Simultaneous determination of uric acid and ascorbic acid using glassy carbon electrodes in acetate buffer solution