Selective amperometric sensing of hydrogen peroxide with Nafion/copper particulates chemically modified electrode

940-945Nafion/copper particulates chemically modified glassy carbon electrode has been prepared by in situ electrochemical deposition. The electrode is found to to be successful for selective amperometric sensing of hydrogen peroxide at -0.2 V vs Ag/AgCl at physiological pH without interference from uric acid, ascorbic acid, catechol, cysteine, nitrite and nitrate. Two linear regions, 20-200 µM and 220-400 µM, for H2O2 detection with the slope and regression coefficient values of 33.2 nA/µM and 25.61 nA/µM and 0.9975 and 0.9999 respectively are obtained with 1.63 µM detection limit (S/N = 3). Application to real samples analysis is demonstrated for milk, urine and tea samples with appreciable recovery values

A new highly conducting carbon black (CL-08) modified electrode functionalized with syringic acid for sensitive and selective L-cysteine electrocatalysis at low potential

Highly selective, sensitive and low potential detection of biological analytes by simple and rapid electrochemical technique using low cost nanocarbons is a demanding research since last decade. Herein, we report a low cost, new, nanocarbon, the carbon black (CL-08) functionalized with syringic acid (SA) modified glassy carbon electrode (GCE) for selective L-cysteine (L-CySH) electrocatalysis at 0.04 V vs Ag/AgCl. The new matrix is competitive in the low potential L-CySH detection compared to the multiwalled carbon nanotube, graphite powder, carbon mesoporous and graphitized mesoporous carbon. The possible in situ generated redox products namely 2,6-dimethoxy benzoquinone and 3,4-dihydroxy-5-methoxy benzoic acid were proposed to form on the GCE/SA@CL-08 with two electron transfer and nernstian behaviours. FTIR and UV–vis analyses collectively revealed the presence of quinone species. The GCE/SA@CL-08 showed L-CySH electrocatalysis with good selectivity, 0.42 nA.μM−1 and 5.4 nA.μM−1 sensitivity in the detection range of 20–100 μM and 100–1000 μM respectively with 639 nM limit of detection, in chronoamperometry. A successful demonstration of L-CySH detection from the simulated blood serum and processed chicken samples with substantial recovery values using the GCE/SA@CL-08 were presented in this study

Selective covalent immobilization of catechol on activated carbon electrodes

Here in, we are reporting simple, selective and direct immobilization of a biological redox mediator, catechol (1,2-dihydroxy phenol, CA), on glassy carbon electrode (GCE) and screen-printed carbon electrode (SPCE) surfaces through electrochemical oxidation procedures in aqueous solutions without any other external matrix. The CA immobilized activated carbon electrodes (GCE*-CA(ads) and SPCE*-CA(ads)) have shown well-defined and stable surface confined redox behavior centered (E(0)') at similar to 0.05 V vs Ag/AgCl and peak-to-peak separation (Delta E(p)) of similar to 20 mV in pH 7 PBS. This observation is selective for CA on the carbon surfaces. Control experiments with other hydroxyl phenols including, Dopamine and Resorcinol failed to show any such adsorption or immobilization on the carbon surfaces. XPS and ATIR/FTIR characterization implies covalent immobilization of the C-4 of the CA through carboxylic functional group of the activated surfaces. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved

Highly selective immobilization of amoxicillin antibiotic on carbon nanotube modified electrodes and its antibacterial activity

An electrochemical route for highly selective immobilization of a beta-lactam family antibiotic, amoxicillin (AMX), from the other drugs, penicillin and ampicillin, on multiwalled carbon nanotube modified glassy carbon electrodes (GCE/AMX@MWNT), without any linkers and surface functionalization, has been successfully demonstrated. The electrochemical response of the AMX on GCE/MWNT showed an irreversible oxidation peak at 0.5 V vs. Ag/AgCl (A1), followed by the growth of a new redox peak at 0 V vs. Ag/AgCl (A2/C2) in pH 7 phosphate buffer solution, which is in parallel to a control phenol electrochemical response, revealed that the phenoxy radical electrogenerated at A1 gets subsequently adsorbed on the underlying MWNT modified electrode with a specific surface confined A2/C2 redox peak with proton-coupled electron transfer behaviour. Physicochemical characterization from X-ray diffraction, transmission electron microscopy and scanning electron microscopy collectively evidenced the immobilization of AMX both on the inner and outer (surface) walls of the carbon nanotubes. Further, the AMX@MWNT hybrid material was found to show enhanced antibacterial activity against three bacterial pathogens, Escherichia coli, Staphylococcus aureus and Bacillus subtilis, over the unmodified AMX and MWNT. Finally, as an environmental pollution remedy, the uptake of the AMX drug from five different simulated sources: river water, sea water, river soil, sea soil and farm milk, was successfully demonstrated by this new electrochemical methodology

Tetracycline Immobilization as Hydroquinone Derivative at Dissolved Oxygen Reduction Potential on Multiwalled Carbon Nanotube

Upon continuous potential cycling of multiwalled carbon nanotube modified electrode (GCE/MWCNT) with Tetracycline antibiotic (Tet) at −0.5 to 0.4 V vs Ag/AgCl in pH 7 phosphate buffer solution, the Tet drug gets selectively immobilized as Tet-hydroquinone derivative (Tet-HQ) on the GCE/MWCNT (GCE/Tet-HQ@MWCNT) and showed a specific surface confined redox peak at E1/2 =−0.24 ± 0.02 V vs Ag/AgCl. Control potential cycling experiment with o-cresol resulted to similar electrochemical characteristic too. But with p-cresol, no such surface confined redox peak was noticed. Dissolved oxygen reduction to hydrogen peroxide (as an intermediate species) at −0.45 V vs Ag/AgCl and its chemical oxidation of the surface bound Tet@MWCNT to Tet-HQ@MWCNT is proposed as a plausible mechanism. Separate ring-disk screen-printed carbon electrode assembly, where MWCNT and a H2O2 detection catalyst (nano-MnO2) modified on the ring and disk respectively, coupled with flow injection analysis showed specific current signals for oxygen reduction reaction at −0.45 V vs Ag/AgCl on the disk and subsequent H2O2 oxidation on ring at 0.8 V vs Ag/AgCl. The surface confined redox system showed highly selective electrocatalytic reduction signal to hydrogen peroxide at ∼0.22 V vs Ag/AgCl without any interference from the ascorbic acid, uric acid, cysteine and nitrite

Selective and low potential electrocatalytic oxidation and sensing of l-cysteine using metal impurity containing carbon black modified electrode

The detection of thiol-containing amino acids, particularly l-cysteine (l-CySH), without any interference from other biochemicals is a challenging research interest in electroanalytical chemistry. Amongst various electrodes, the nanogold modified electrode has been reported to be effective for low potential electrochemical oxidation (∼0 V vs. Ag/AgCl) and sensing of l-CySH. Herein, we report a conductive carbon black (CB, CL-08) modified glassy carbon electrode (GCE/CL-08) with a high surface area (1000 m2 g-1), prepared by a simple drop-casting technique for efficient electrocatalytic oxidation at the lowest oxidation potential, -0.13 V vs. Ag/AgCl, and sensing of l-CySH in a pH 6.65 phosphate buffer solution. The trace metal impurities such as Ni (0.18 wt%) and Fe (0.42 wt%) in CL-08 are found to be key for such unique and unusual electrocatalytic property observed in this study. Compared with the multiwalled carbon nanotube and graphite powder modified electrodes, the GCE/CL-08 showed about 400 mV reduction in the oxidation potential and twenty times enhancement in the current signal for the CySH. A chronoamperometry detection of l-CySH on the GCE/CL-08 at an applied potential = -0.13 V vs. Ag/AgCl yielded a current linearity from 50 to 700 μM with a LOD = 45.87 nM. There are no interferences by common biochemicals such as ascorbic acid, dopamine, uric acid, xanthine, hypoxanthine and homo-cysteine on the l-CySH oxidation potential. Selective chronoamperometric detection of l-CySH in the blood serum demonstrated ∼100% recovery value as a validation for the present protocol

Cosmetic Hydrogen Peroxide Detection Using Nano Bismuth Species Deposited Built-in Three-in-One Screen-Printed Silver Electrode

A built-in three-in-one screen-printed electrode assembly containing nano bismuth species deposited silver as working, pre-oxidized silver as reference and unmodified silver as counter electrodes (designated as SPAgE-Bi(nano)), has been developed for simple electrochemical sensing of H(2)O(2) in pH 7 phosphate buffer solution. The working electrode showed similar to 250 mV reduction in over-potential and a two-fold increased peak current values for electrocatalytic reduction of H(2)O(2) over the respective unmodified silver working electrode (i.e. SPAgE) following a diffusion-controlled electron-transfer mechanism. 50 nm sized Bi particles on SPAgE surface was seen in SEM picture of the working electrode. Linear range of H(2)O(2) detection from 100 mu M to 5 mM, a sensitivity of 0.627 mu A/mM and detection limit (S/N = 3) of 56.59 mu M were obtained. Finally, SPAgE-Bi(nano) sensor assembly was utilized for cosmetic H(2)O(2) determination, where obtained values and labeled values were in good agreement with recovery in the range of 94.75-101.03 %

Flow Injection Analysis of Aluminum Chlorohydrate in Antiperspirant Deodorants Using a Built-in Three-in-one Screen-Printed Silver Electrode

A screen-printed silver strip with a built-in three-in-one electrode (SPAgE) configuration of Ag-working, Ag-counter and Ag/Ag(x)O (silver oxides) pseudoreference electrodes has been developed for sensitive and selective electrochemical flow injection analysis (FIA) of aluminum chlorohydrate (ACH) present in antiperspirants, through the free Cl(-) ion liberated from ACH in aqueous medium, as a redox signal at Ag-working electrode in pH 6 phosphate buffer solution (PBS). The solution phase and instrumental parameters were systematically optimized. The calibration graph was linear in the window 1-200 ppm concentration of ACH and the lowest detection limit (S/N = 3) was 295 ppb with a slope of 0.0989 mu A/ppm and regression coefficient of 0.998. Calculated relative standard deviation (RSD) values for the detection of 5 and 50 ppm ACH by this method are 2.21% and 2.16%, respectively. Four different antiperspirant deodorants real samples with and without ACH content were successfully analyzed and the detected values obtained were found to be in good agreement with the product labeled values

A new electro-generated o-dianisidine derivative stabilized MWCNT-modified GCE for low potential gallic acid

The exploration of functional group interactions and electro-generated species stabilization on chemically modified electrodes for efficient electro-analytical application is a continuing research area in electrochemistry. In addition, the electrochemical behaviours of the intermediate species, which are generated from the aromatic organic redox mediator and possess both methoxy and amine functional groups, have been rarely studied for electro-analytical applications. For the first time, we report the stabilization of an electro-generated enone derivative of the o-dianisidine (EDo-D) dimer formed as one of the intermediate species during o-dianisidine immobilization. The electro-generated o-dianisidine derivative (o-DD)-stabilized multi-walled carbon nanotube (MWCNT)-modified glassy carbon electrode (GCE/o-DD@MWCNT) exhibited two highly reproducible and, well-defined surface-confined redox couples in a pH 7 phosphate buffer solution (PBS). FTIR analyses indicated the presence of an amine group linkage and an azo product in the o-DD@MWCNT hybrid. UV-Vis and GC-MS analyses confirmed the presence of o-dianisidine in its azo dimer form within the MWCNT. In addition, the enone derivative of the o-dianisidine dimer present on the GCE/o-DD@MWCNT successfully sensed gallic acid (GA) at 0.16 V vs. Ag/AgCl in pH 7 PBS. Highly selective GA detection was achieved with a sensitivity of 0.4580 µA µM-1, a detection range of 100-1300 µM and a detection limit of 144 nM using chronoamperometry. GCE/o-DD@MWCNT also demonstrated effective GA detection in simulated real grape juice and water samples

Evaluation of radical scavenging capacity of polyphenols found in natural malaysian honeys by voltammetric techniques

As minor constituents present in natural honey, polyphenols have the capacity as antioxidant by donating electron to halt detrimental actions of free radicals. The present work aims to analyze the electrochemical behaviour of polyphenols identified in Malaysian Apis and Trigona honey samples, determine and compare their reducing strengths as well as qualitatively evaluate the radical scavenging capacity of these phenolics in Malaysian honey samples. Six flavonoids, eight phenolic acids, and tannin pentagalloyl glucose (PGG) dissolved in 0.1 M PBS pH 7 were studied by cyclic voltammetry (CV). Seventeen Malaysian honey samples were analyzed using differential pulse voltammetry (DPV). Cyclic voltammograms revealed that polyphenols with catechol moiety in their structure exhibited Ep1a at low potentials, ranging between +0.173 V and +0.404 V. PGG and quercetin may have equal tendency to donate electron (same Ep1a) but higher peak current was observed for the former indicates its higher reducing strength, suggesting PGG as the strongest antioxidant among studied polyphenols. From DP voltammograms, oxidation of honey phenolics occurred in all honey samples with predominant catechol-bearing peak P1 observed in nanas N1, kelulut K3 and tualang T1 honeys. The varied peak current intensities observed for P1-P3 in all analyzed Malaysian honey samples suggested that these honey samples can act against free radicals at varying degree and thus are good sources of natural antioxidants