Modified Paste Electrode Research Articles

Determination of nanomolar lead (II) using H2O2-oxidized activated carbon modified electrode

The virgin activated carbon (AC) was oxidized by 30% H2O2 under the ultrasonic condition for 6 h (denoted as AC-6). The electrochemical response of Pb2+ at the AC-6 modified paste electrode was investigated, suggesting that AC-6 shows much higher accumulation efficiency to trace levels of Pb2+. Based on this, a sensitive and convenient electrochemical method was developed for the determination of Pb2+ utilizing the excellent properties of AC-6. In pH 3.6 HAc-NaAc buffer, Pb2+ was easily accumulate at the surface of AC-6 modified paste electrode, then reduced to Pb at −1.20 V. During the following anodic sweep, the reduced Pb was oxidized and resulted in an oxidation stripping peak at −0.58 V. The stripping peak current is proportional to the concentration of Pb2+ over the range from the 8.0 × 10−9 to 2.0 × 10−6 mol l−1, and the limit of detection is as low as 2.0 × 10−9 mol l−1. Finally, this newly-developed method was successfully employed to determine Pb2+ in water samples.

Determination of cadmium (II) using H2O2-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H2O2 under ultrasonic conditions. Compared with pristine AcC, the H2O2-oxidized AC possesses higher accumulation ability to trace levels of Cd2+. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd2+. In 0.01 mol L−1 HClO4 solution, Cd2+ was effectively accumulated at the surface of H2O2-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd2+ changes linearly with concentration over the range 5.0 × 10−8 to 5.0 × 10−6 mol L−1. The limit of detection was found to be 3.0 × 10−8 mol L−1 for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd2+ in waste water samples.

Carbon Electrodes Modified by Nanoscopic Iron(III) Oxides to Assemble Chemical Sensors for the Hydrogen Peroxide Amperometric Detection

AbstractIn this study we show that nanoparticles of various ferric oxides (hematite, maghemite, amorphous Fe2O3, β‐Fe2O3 and ferrihydrite) incorporated into carbon paste exhibit electro‐catalytic properties towards hydrogen peroxide reduction. The modified paste electrode performances were evaluated and compared with those obtained with Prussian Blue‐modified carbon paste electrode, which represents an excellent chemical mediator towards the H2O2 redox reaction (as widely described in literature). The best catalytic activity was found for carbon paste modified by amorphous ferric oxide with 2–4 nm particle size, which was further tested for possible application as hydrogen peroxide sensor. At pH 7, the limit of detection was 2×10−5 M H2O2 (S/N=3), the calibration curves were linear upto 8.5 mM H2O2 (R2=0.998), the measurement reproducibility (RSD=97%, n=4), the interelectrode reproducibility (RSD=16%, nelectrodes=5) and <3 s response time.

Enhanced Electrochemical Detection of DNA Hybridization with Carbon Nanotube Modified paste Electrode

A novel electrochemical genesensor using twice hybridization enhancement of gold nanoparticles based on carbon paste modified electrode is described. The carbon nanotube modified carbon paste electrode (CNTPE) and mesoporous molecular sieve SBA-15 modified carbon paste electrode (MSCPE) were investigated. The assay relies on the immobilization of streptavidin-biotin labeled target oligonucleotides onto the electrode surface and its hybridization to the gold nanoparticle-labeled DNA probe. After twice hybridization enhanced connection of gold nanoparticles to the hybridized system, the differential pulse voltammetry (DPV) signal of total gold nanoparticles was monitored. It was found that the adsorption of oligonucleotide and hybridized DPV signal on CNTPE were both enhanced in comparison with that of pure carbon paste electrode (CPE). But this trend was reverse on MSCPE. The DPV detection of twice hybridized gold nanoparticles indicated that the sensitivity of the genesensor enhanced about one order of magnitude compared with one-layer hybridization. One-base mismatched DNA and complementary DNA could be distinguished clearly. However, no distinct advantage of MSCPE over CPE was found.

Electrocatalysis and Determination of Ascorbic Acid Through Graphite Paste Electrode Modified With Iron Nitroprusside

Iron nitroprusside, Fe(II)NP was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified electrode, Fe(II)NP showed two redox couples (E½ ox )1 = 0.24 and (E½ ox )2 = 0.85 V vs. SCE attributed to Fe (II) /Fe (III) and Fe (II) (CN)5NO / Fe (III) (CN)5NO, respectively. The redox couple at (E½ ox )1 = 0.24 V presents an electrocatalytic response for ascorbic acid. The modified paste electrode exhibits a decrease of 180 mV in the ascorbic acid oxidation. The modified graphite paste electrode gives a linear range from 1.0 × 10 -3 to 2.6 × 10 -2 mol L -1 of ascorbic acid with a detection limit of 1.4 × 10 -3 (±1.2%) mol L -1 (n =3). The electrocatalytic oxidation of ascorbic acid compounds by the mediator has been used for the determination of ascorbic acid in a commercially pharmaceutical available product.

Functionalized Ormosils-Based Biosensor: Probing a Horseradish Peroxidase-Catalyzed Reaction

We report herein the electrochemistry of redox materials encapsulated within organically modified sol-gel glasses (ormosil). The ormosils that encapsulated ferrocene monocarboxylic acid and potassium ferricyanide are made using palladium-linked 3-glycidoxypropyltrimethoxysilane, trimethoxysilane, HCl, and an aqueous solution of potassium ferricyanide or ferrocene monocarboxylic acid followed by gelation of the same for 24 h at 30°C. The requirement of palladium linkage with ormosil is also examined and data on the electrochemistry of (i) only potassium-ferricyanide encapsulated ormosil without palladium, (ii) potassium-ferricyanide encapsulated ormosil with varying concentrations of palladium are reported. The ormosil made with optimum concentrations of palladium shows better redox electrochemistry as compared to that made without palladium. The ormosils are converted into fine powder followed by incorporation together with horseradish peroxidase within a graphite paste electrode. The peroxide biosensors based on modified-paste electrodes are characterized by cyclic voltammetry and chronoamperometry. Results on electrochemical sensing of hydrogen peroxide close to the cathodic peak potential of potassium ferricyanide and ferrocene monocarboxylic acid are reported. The performance of these peroxide biosensors is discussed and compared to those reported earlier. © 2003 The Electrochemical Society. All rights reserved.

An ormosil-based peroxide biosensor — a comparative study on direct electron transport from horseradish peroxidase

An ormosil-based peroxide biosensor, based on direct electron transfer from horseradish peroxidase (HRP) encapsulated within ormosil in the presence of peroxide is reported. The HRP is immobilized within two different matrixes: (1) graphite paste electrode and (2) a new organically modified sol–gel glass (ormosil) electrode. The direct electron transfer from these two matrixes has been studied based on cyclic voltammetry and amperometric measurement. In both cases, direct electron transfer takes place between 0.1 and −0.2 V versus Ag/AgCl, however, the direct bioelectrochemical response of HRP is influenced by direct reduction of peroxide even in the absence of HRP at −0.2 V versus Ag/AgCl, whereas, direct bioelectrochemical response of biosensor at 0.05 V versus Ag/AgCl is only the function of enzymatic reaction. The mass transfer kinetics within these two matrixes have been analysed using the data on cyclic voltammograms of soluble ferrocene at the surface of paste and ormosil modified electrodes. The data on peak current versus square root of scan rate shows linear relation and passes through origin while using HRP modified paste electrode, whereas, the same has positive intercept while using ormosil modified peroxide biosensor suggesting well-behaved diffusion limited conditions within paste matrix and poor diffusion kinetics of mass-transport within ormosil matrix. The ormosil-based peroxide biosensor is developed using a bilayer of ormosil within which HRP is sandwiched between two layers. The new ormosil matrix with and without encapsulated HRP is analyzed by scanning electron microscopy (SEM). The HRP encapsulated ormosil electrode shows greater than 90% reproducible response for more than 3 months when stored in dry condition at 4°C. The typical calibration curves on the subsequent additions of peroxide of ormosil-based biosensor at 0.05 V versus Ag/AgCl and at −0.2 V versus Ag/AgCl are reported. The various parameters such as inhibition of peroxidase at higher peroxide concentrations, direct reduction of peroxide near −0.2 V versus Ag/AgCl, the kinetics of electron transfer due to direct oxidation of peroxide at 0.7 V versus Ag/AgCl on bare glassy carbon electrode, and direct electron transfer from enzymatically oxidized peroxidase are discussed.

Sensitivity, Selectivity and Reproducibility of Some Mediated Electrochemical Biosensors/sensors

Comparative studies on the mediated electrochemical response of tetracyanoquinodimethane (TCNQ), tetrahiafulvalene (TTF) and dimethyl ferrocene (dmFc) modified paste electrodes are reported based on cyclic voltammetry and amperometric measurements. The studies have been conducted on the graphite paste electrodes of different composition mainly; i) graphite and mediators (TCNQ/TTF/dmFc) paste only, ii) graphite, glucose oxidase and mediators (TCNQ/TTF/dmFc) modified paste, and iii) graphite, mediators (TCNQ/TTF/dmFc) and peroxidase modified paste. The results on the mediated electrochemical oxidation of NADH and glucose on the systems i–ii are reported. The cyclic voltammetry response of the systems i and ii for subsequent 15 cycles between -0.2 to 0.5 V Vs Ag/AgCl has been examined at a scan rate of 5 mV/s. The electrochemical oxidation of NADH has been studied on system i, whereas mediated electrochemical oxidation of glucose has been studied on system ii. The results suggest that TCNQ is a better mediator for probing NADH and glucose oxidase catalyzed reactions. The mediated electrochemical probing of peroxide has been studied on the system iii. The results suggest that TTF is better mediator for probing peroxidase catalyzed reaction. The selectivity of the mediated electrochemical response of systems ii and iii has been studied based on the amperometric and voltammetric measurements of glucose and peroxide on systems ii and iii followed by the addition of ascorbic acid. The results show that mediated electrochemical responses of these systems at both anodic and cathodic potentials are significantly affected due to the mediated and direct oxidation of ascorbic acid. The sensitivity of these systems to ascorbic acid is due to the occurrence of both mediated and non-mediated electrochemical oxidation of ascorbic acid. The ascorbic acid is oxidized through the mediated mechanism at the anodic potential of the mediators and is directly oxidized at the cathodic potentials of the mediator. A typical response curve of the oxidation of glucose and peroxide on systems ii and iii are reported, followed by addition of ascorbic acid in order to understand the reliability of the mediated electrochemical detection of glucose in the presence of ascorbic acid.

Ethanol Biosensors and Electrochemical Oxidation of NADH

Comparative studies of the electrochemical oxidation of reduced nicotinamide coenzyme (NADH) at the surfaces of chemically modified graphite paste electrodes (CMEs) are reported. Three different electroactive materials, tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), and dimethyl ferrocene (dmFc), were used to construct three different chemically modified paste electrodes. The oxidation of NADH was examined on the basis of cyclic voltammetric measurements. The results show that all three mediators (TCNQ, TTF, and dmFc) behave as efficient mediators of the oxidation of NADH. The typical response curves of NADH at the CMEs surfaces are reported. Incorporating alcohol dehydrogenase and electroactive materials (TCNQ, TTF, and dmFc) within the graphite paste electrodes has led to the development of ethanol biosensors. Typical response curves for the ethanol analysis are reported. Comparative studies on the mediated electrochemical responses of the biosensors to ethanol are discussed.

A comparative study of Prussian-Blue-modified graphite paste electrodes and solid graphite electrodes with mechanically immobilized Prussian Blue

The cyclic voltammetry of Prussian Blue was studied using two different types of electrodes. In one case microcrystalline particles of Prussian Blue were mechanically immobilized on the surface of a paraffin-impregnated solid graphite electrode, whereas in the other the Prussian Blue was added to a paste of graphite and silicone oil. The overall behaviour of Prussian Blue in both electrodes is very similar to the well-known behaviour for electrodes with an electrochemically synthesized Prussian Blue film. Differences were observed for the modified paste electrode, particularly in acid-containing solutions. Prussian Blue exhibits pronounced ion-exchange properties in acid solutions. New voltammetric peaks are observed which are clearly related to an exchange of protons between Prussian Blue and the solution. In mixed solutions containing potassium ions and protons competition between these cations is visible. Scanning electron microscopy in conjunction with energy dispersive X-ray analysis supports a reaction scheme which includes both cations. This study provides evidence for the ability of protons to undergo a chemically reversible intercalation in the Prussian Blue lattice. An additional aim of this study was to assess the reliability of experiments using graphite paste electrodes with an organic binder. The results show that the binder affects the electrochemistry of Prussian Blue, but the similarities between “pure” Prussian Blue and that in the paste electrode are clearly dominant.