B.N. Chandrashekar

Sol–gel immobilized biosensor for the detection of organophosphorous pesticides: A voltammetric method

Organophosphorous compounds are important neuroactive molecules whose presence exhibits significant analytical challenges. An acetylcholinesterase (AChE) based amperometric biosensor was developed by silica sol-gel film immobilization of the enzyme onto the carbon paste electrode. The mono enzyme biosensor was used for the determination of two organophosphorous compounds such as methyl parathion (MP) and acephate in 0.1M phosphate buffer (pH 7.0). The substrate used was acetylthiocholine chloride (ASChCl) confirmed the formation of thiocholine and it was electrochemically oxidized giving significant increase in anodic peak current around at 0.60 V versus calomel electrode. The influence of pH, enzyme loading and substrate concentration on the response of the biosensor was investigated. The monoenzyme biosensor provided linearity to methyl parathion and acephate in the concentration range of 0.1-0.5 ppb and 50-750 ppb with an incubation time of 20 min and 4 min. The detection limits under the optimum working conditions were found to be 0.08 ppb for methyl parathion and 87 ppb for acephate. The sensor shows good operational stability 89% of its original activity for 60 successive measurements.

Electropolymerisation of l-arginine at carbon paste electrode and its application to the detection of dopamine, ascorbic and uric acid

L-arginine was electropolymerised on a carbon paste electrode (CPE) to form the biopolymer by free radical formation in the electro oxidation process of the amino and carboxylic group containing compound by cyclic voltammetric technique. The modified electrode shows an excellent electrocatalytic activity towards the oxidation of both dopamine (DA) and ascorbic acid (AA). It was demonstrated that the deposited biopolymer has positive charges over the bare carbon electrode surface, which leads to the formation of electrical double layer made the fast electron transfer process could leads to the diffusion of dopamine, ascorbic acid and uric acid on their charge gradient by cyclic voltammetric technique. The response of the sensor was tested towards the different dopamine concentration. The catalytic peak current obtained was linearly related to DA concentrations in the ranges of 5×10(-5) to 1×10(-4)M L(-1) with correlation co-efficient of 0.9924 which reveals the adsorption controlled process. The detection limit for dopamine was 5×10(-7)M L(-1). The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid (AA) and response is fast stable, reliable, resistant to biofouling and can be applied for the real sample analysis in medical, pharmaceutical and biotechnological sectors. The adsorption-controlled process and kinetic parameters of the poly(L-arginine) were determined using electrochemical approaches.

Simultaneous cyclic voltammetric determination of norepinephrine, ascorbic acid and uric acid using TX-100 modified carbon paste electrode

A sensitive and selective electrochemical method for the determination of norepinephrine (NE) using TX-100 modified carbon paste electrode was developed. The TX-100 modified carbon paste electrode shows excellent electrocatalytic activity towards the oxidation of NE in phosphate buffer solution (pH 7.0). The linear range of 0.5 × 10−4 to 2.0 × 10−4 M and detection limit of 5 × 10−6 M were observed at pH 7.0 phosphate buffer solution. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The separation of the oxidation peak potentials for NE–AA and NE–UA were about 0.16 V and 0.11 V, respectively. The differences were large enough to determine AA, NE and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect norepinephrine in the presence of ascorbic acid and uric acid in physiological samples.