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

Abstract

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.