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

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

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

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

Enhanced wide-range monotonic piezoresistivity, reliability of Ketjenblack/deproteinized natural rubber nanocomposite, and its biomedical application

Piezoresistive behavior of 6 to 9 wt % Ketjenblack-reinforced deproteinized natural rubber (KB/DPNR) nanocomposite developed by two-roll mill was studied under compressive pressure (0 to 12.54 MPa). The 6 wt % KB/DPNR exhibited monotonic piezoresistivity, the highest electrical resistance change (485%), remarkable reversibility and minimal hysteresis. Furthermore, a good sensitivity (S) = 1.1 MPa−1 for 0.25 to 2.49 MPa, high test–retest reliability (intraclass correlation co-efficient, ICC = 0.99) under 0 to 2.49 MPa for three repetitions conducted at an interval of 24 h and excellent repeatability (standard deviation, SD = 4.8%) to a swing of 6.25 MPa for 50 cyclic compression were achieved. Homogeneous dispersion and high aspect ratio of KB and higher chemical linkage (due to double crosslinking agents) between KB and DPNR may be responsible for the enhanced piezoresistivity. For practical application, the KB/DPNR was interfaced with the microcontroller through a bridge rectifier via custom-built Simulink and successfully monitored finger pressure in real time during bone movement on human

Fabrication, characterization and application of laccase–nylon 6,6/Fe3+ composite nanofibrous membrane for 3,3′-dimethoxybenzidine detoxification

In this study, laccase was immobilized on nylon 6,6/Fe3+composite (NFC) nanofibrous membrane and used for the detoxification of 3,3′-dimethoxybenzidine (DMOB). The average size and tensile strength of the NFC membrane were found to be 60–80 nm (diameter) and 2.70 MPa, respectively. The FTIR results confirm that the amine (N–H) group of laccase was attached with Fe3+particles and the carbonyl (C=O) group of NFC membrane via hydrogen bonding. The half-life of the laccase–NFC membrane storage stability was increased from 6 to 11 weeks and the reusability was significantly extended up to 43 cycles against ABTS oxidation. Enhanced electro-oxidation of DMOB by laccase was observed at 0.33 V and the catalytic current was found to be 30 µA. The DMOB-treated mouse fibroblast 3T3-L1 preadipocytes showed maximum (97 %) cell inhibition at 75 µM L−1within 24 h. The cytotoxicity of DMOB was significantly decreased to 78 % after laccase treatment. This study suggests that laccase–NFC membrane might be a good candidate for emerging pollutant detoxification