Square Wave Voltametry Research Articles

Simultaneous electro-chemical detection of Pb and Fe by copper-modified carbon paste electrode in the portion of soil

A carbon graphite and copper powder paste electrode (CPE-Cu) was successfully designed as a working electrode for electrochemical analysis. The structural characteristics of this electrode were revealed by X-ray diffraction. Voltammetric techniques and electrochemical impedance spectroscopy were used to assess the electroactivity of the proposed working electrode. X-ray diffraction showed that the composite material has a slightly different crystalline structure to pure graphite, since the copper modification influenced the angles of reflection so that they fluctuated towards slightly larger values. The study of the electrochemical behaviour of the CPE-Cu electrode using cyclic voltammetry showed that the redox phenomena at the electrode surface are almost reversible. Analysis of the soil portion using cyclic voltammetry showed that lead (II) and iron (II) showed current peaks at potentials −0.36 V and +0.12 V respectively. These potentials were confirmed by square-wave voltametry. Cyclic voltammetry and square wave voltammetry showed linearity between the portion of soil in the soil and the electrochemical response. In addition, the study of the effect of the scanning speed showed that the reactions at the working electrode are controlled by a diffusion phenomenon at the surface of the working electrode. Electrochemical impedance spectroscopy showed that the electrode material had a low resistance to charge transfer, with a complete analysis of around 80 ohm.cm2. The heavy metals Cd2+, Pb2+ and Fe2+ were detected simultaneously at trace levels. Calculations of the detection limits for Pb2+ and Fe2+ gave 0.709 ppm and 0.821 ppm respectively. At the end of this work, it can be said that the proposed sensor can be used as an instrument for monitoring the metals studied, as the detection limits were relatively low despite the complexity of the detection medium (portion of soil).

Mesoporous Silica Thin Films for Improved Electrochemical Detection of Paraquat

An electrochemical method was developed for rapid and sensitive detection of the herbicide paraquat in aqueous samples using mesoporous silica thin film modified glassy carbon electrodes (GCE). Vertically aligned mesoporous silica thin films were deposited onto GCE by electrochemically assisted self-assembly (EASA). Cyclic voltammetry revealed effective response to the cationic analyte (while rejecting anions) thanks to the charge selectivity exhibited by the negatively charged mesoporous channels. Square wave voltametry (SWV) was then used to detect paraquat via its one electron reduction process. Influence of various experimental parameters (i.e., pH, electrolyte concentration, and nature of electrolyte anions) on sensitivity was investigated and discussed with respect to the mesopore characteristics and accumulation efficiency, pointing out the key role of charge distribution in such confined spaces on these processes. Calibration plots for paraquat concentration ranging from 10 nM to 10 μM were constructed at mesoporous silica modified GCE which were linear with increasing paraquat concentration, showing dramatically enhanced sensitivity (almost 30 times) as compared to nonmodified electrodes. Finally, real samples from Meuse River (France) spiked with paraquat, without any pretreatment (except filtration), were analyzed by SWV, revealing the possible detection of paraquat at very low concentration (10-50 nM). Limit of detection (LOD) calculated from real sample analysis was found to be 12 nM, which is well below the permissible limits of paraquat in drinking water (40-400 nM) in various countries.

Electrochemical Evaluation of the Antioxidant Capacity of Phenolic Compounds in Virgin Olive Oil

Cyclic voltametry (CV) and Square wave voltametry (SWV) were used to study the electrochemical behavior and evaluate the antioxidant capacity of virgin olive oil. Firstly, in this work we illustrate the electrochemical methods based on the preparation and characterization of H2O2 amperometric sensor, then the antioxidant capacity of the virgin olive oil was evaluated by measuring of the of virgin olive oil effect on the H2O2 reduction.

A highly sensitive square wave voltammetry based biosensor for kinase activity measurements.

An electrochemical biosensor has been developed for ultrasensitive, label-free determination of protein kinase activity. The sensor is composed of a unique peptide monolayer on a gold electrode. It identifies the order change in the monolayer upon phosphorylation, via square wave voltametry (SWV) measurements. Disorder caused by the introduction of the phosphate groups onto the middle of the peptide sequence results in pinhole formation and therefore an increase in the electrochemical signal. The measured sensitivity was 100 nM of kinase and the dynamic range was 100 nM up to 11 μM. Sensitivity was an order of magnitude higher, and the dynamic range wider by two orders of magnitude, as compared to our previously reported impedimetric method, in which the sensitivity was 1 μM, and the dynamic range was 1-20 μM.

A nanocoaxial-based electrochemical sensor for the detection of cholera toxin.

Sensitive, real-time detection of biomarkers is of critical importance for rapid and accurate diagnosis of disease for point of care (POC) technologies. Current methods do not allow for POC applications due to several limitations, including sophisticated instrumentation, high reagent consumption, limited multiplexing capability, and cost. Here, we report a nanocoaxial-based electrochemical sensor for the detection of bacterial toxins using an electrochemical enzyme-linked immunosorbent assay (ELISA) and differential pulse voltammetry (DPV) or square wave voltametry (SWV). The device architecture is composed of vertically-oriented, nanoscale coaxial electrodes in array format (~10(6) coaxes per square millimeter). The coax cores and outer shields serve as integrated working and counter electrodes, respectively, exhibiting a nanoscale separation gap corresponding to ~100 nm. Proof-of-concept was demonstrated for the detection of cholera toxin (CT). The linear dynamic range of detection was 10 ng/ml-1 µg/ml, and the limit of detection (LOD) was found to be 2 ng/ml. This level of sensitivity is comparable to the standard optical ELISA used widely in clinical applications, which exhibited a linear dynamic range of 10 ng/ml-1 µg/ml and a LOD of 1 ng/ml. In addition to matching the detection profile of the standard ELISA, the nanocoaxial array provides a simple electrochemical readout and a miniaturized platform with multiplexing capabilities for the simultaneous detection of multiple biomarkers, giving the nanocoax a desirable advantage over the standard method towards POC applications.

A verapamil electrochemical sensor based on magnetic mobile crystalline material-41 grafted by sulfonic acid

Magnetic (Fe2O3) mobile crystalline material-41 (MCM-41) grafted by sulfonic acid (Fe2O3-MCM-41-SO3H) was prepared and characterized using transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and square wave voltametry (SQWV) used to investigate the electrochemical behavior of verapamil at the sulfonic acid functionalized magnetic mesoporous silica, which was modified through carbon paste electrode (Fe2O3-MCM-41-SO3H-CPE). The Fe2O3-MCM-41-SO3H-CPE showed better performance for the electrochemical oxidation of verapamil, when compared with bare carbon paste electrode (CPE) and Fe2O3-MCM-41-CPE. The experimental conditions influencing the determination of verapamil were optimized and under optimal conditions, the oxidation peak current was proportional to verapamil concentration in the range of 50–160 and 160–350nmoldm−3, while the detection limit was 41nmoldm−3 (S/N=3). The proposed method was successfully applied to determine verapamil in human serum, yielding satisfactory results. The spiked recoveries were in the range of (94.5–104.1%).

Graphene patterned polyaniline-based biosensor for glucose detection

This paper describes a glucose electrochemical biosensor, layer-by-layer fabricated from graphene and polyaniline films. Graphene sheets (0.5×0.5 cm 2) with the thickness of 5 nm (15 layers) were synthesized by thermal chemical vapor deposition (CVD) under ambient pressure on copper tapes. Then they were transferred into integrated Fe 3 O 4-doped polyaniline (PANi) based microelectrodes. The properties of the nanocomposite films were thoroughly characterized by scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM) and electrochemical methods, such as square wave voltametry (SWV) and chronoamperometry. The above graphene patterned sensor (denoted as Graphene/Fe 3 O 4/PANi/GOx) shows much improved glucose sensitivity (as high as 47 μA mM −1 cm −2) compared to a non-graphene one (10–30 μA mM −1 cm −2, as previously reported in the literature). It can be expected that this proof-of-concept biosensor could be extended for other highly sensitive biodetection.

Electrochemical behavior and square wave voltammetric determination of aristolochic acid-I

Electroanalytical procedure for the determination of nephrotoxic aristolochic acid-I in the medicinal plant has been developed in the presence of potential interferences of lead and cadmium by square wave voltametry (SWV). Among the phosphate buffers of pH values at 5.0, 6.1, 6.5 and 7.0, the phosphate buffers of pH 6.1 yielded the most accurate analysis of AA-I in the presence of Pb2+ and Cd2+; Pb2+ was precipitated as Pb(HPO4) and did not appear in the SW voltammogram, while Cd2+ appeared at -0.564 V which was well resolved from AA-I at -0.416 V. When the Ip of AA-I was plotted vs. concentrations between 1.67 x 10(-8) M and 1.67 x 10(-6) M in the presence of Pb2+ and Cd2+, a linear calibration curve was obtained with a slope of 6 x 10(8) nA/M and a correlation coefficient of 0.9999. The present method was applied to determine AA in the dried natural products of Aristolochia contorta Bunge; Total AA in the dried root and the ripe fructus of Aristolochia contorta Bunge were found as 25 +/- 1 microg/g and 85 +/- 3 microg/g, respectively.

Electrochemical detection of 17β-estradiol using DNA aptamer immobilized gold electrode chip

An electrochemical detection method for chemical sensing has been developed using a DNA aptamer immobilized gold electrode chip. DNA aptamers specifically binding to 17β-estradiol were selected by the SELEX (Systematic Evolution of Ligands by EXponential enrichment) process from a random ssDNA library, composed of approximately 7.2 × 10 14 DNA molecules. Gold electrode chips were employed to evaluate the electrochemical signals generated from interactions between the aptamers and the target molecules. The DNA aptamer immobilization on the gold electrode was based on the avidin–biotin interaction. The cyclic voltametry (CV) and square wave voltametry (SWV) values were measured to evaluate the chemical binding to aptamer. When 17β-estradiol interacted with the DNA aptamer, the current decreased due to the interference of bound 17β-estradiol with the electron flow produced by a redox reaction between ferrocyanide and ferricyanide. In the negative control experiments, the current decreased only mildly due to the presence of other chemicals.

Direct Electrochemistry and Raman Spectroscopy of Sol−Gel-Encapsulated Myoglobin

The direct electrochemistry of myoglobin (Mb) has been observed at a glassy carbon (GC) electrode coated with silica sol-gel-encapsulated Mb film. A well-behaved cyclic voltammogram is observed with a midpoint potential (E(1/2)) of -0.25 V vs Ag/AgCl in a pH 7.0 phosphate buffer. This potential, which is pH-dependent, is 70-90 mV more negative than the formal potential values obtained by using the spectroeletrochemical titration method at the same pH. Square wave voltametry (SWV) also shows a peak potential of -0.25 V for the reduction of Mb under the same experimental conditions. Both cathodic and anodic peak currents have a linear relationship with the scan rate. The midpoint potential decreases with pH, having a slope of -30 mV/pH. UV-vis and resonance Raman spectroscopic studies reveal that the sol-gel provides a bio-compatible environment where Mb retains a structure similar to its solution form, a 6-coordinated aquomet myoglobin. These results suggest that the silica sol-gel is a useful matrix for studying direct electrochemistry of other heme proteins.

Enhanced application of square wave voltammetry with glassy carbon electrode coupled to multivariate calibration tools for the determination of B 6 and B 12 vitamins in pharmaceutical preparations

Vitamins B 6 (VB 6) and B 12 (VB 12) were simultaneously determined in pharmaceutical preparations by using square wave voltametry (SWV) together with artificial neural networks (ANNs). Supporting electrolyte solution, pH and voltametric technique were optimised. The calibration set was built with several artificial samples containing both active ingredients and excipients. Deviations from linearity were observed for both analytes. It is probably due to interactions among the electro active components and competition by the electrode surface, fact that supports the use of ANNs. Recoveries when analysing a nine sample validation set, of 100.2 and 96.4 were calculated for VB 6 and VB 12, respectively. Commercial samples were analysed with reasonably good results considering the complexity of the mixture studied.

Differentiating the orientations of photosynthetic reaction centers on Au electrodes linked by different bifunctional reagents

The photosynthetic reaction center (RC) composite film was fabricated by self-assembled monolayers (SAMs) on the Au electrode with two different bifunctional reagents, 4-aminothiophenol (ATP) and 2-mercaptoethylamine (MEA), respectively. The square wave voltametry (SWV), bulk electrolysis and photocurrent test were employed for characterizing the composite film. The dramatic different electrochemical characteristics were observed for the two types of films, which strongly suggested an orientational difference for RC arising from the structural difference between the two bifunctional reagents. For RC-MEA film, three redox peaks which implying electron transfer (ET) between the primary donor (P) and the bacteriopheophytin (Bphe) were observed. While for RC-ATP film, two redox peaks implying ET between the nonheme iron and the primary quinone (Q A) were observed. The ET behavior driven by electric field also supported the result that the RC could be linked to the electrode at different sites. The site-specific immobilization approach reported here supplies a method to differentiate the protein orientation.

Thin-layer square wave voltammetry and square wave stripping voltammetry

The feasibility of combining the highly sensitive techniques of square wave voltametry (SWV) and square wave stripping voltametry (SWSV) with a commercially available thin-layer electrochemical cell having a single-working electrode is demonstrated. The characteristics of thin-layer SWV were investigated by using ferri-/ferrocyanide and diazepam (Valium) systems. The calibration plot data for diazepam are linear between 10 and 60 ppm with a detection limit of 0.06 ppm. With a Hg-coated glassy carbon electrode, SWSV studies were carried out on 30-..mu..L aqueous solutions of In/sup 3 +/ and Pb/sup 2 +/ ions. The calibration curve for In/sup 3 +/ is linear up to 2000 ppb with a detection limit of 8 ppb. The detection limit for lead is 11 ppb.