SENSITIVITY, SELECTIVITY AND REPRODUCIBILITY OF SOME MEDIATED ELECTROCHEMICAL BIOSENSORS SENSORS/

Comparative studies on the mediated electrochemical response of tetrac yanoquinodimethane (TCNQ), tetrathiafulvalene (TTF) and dimethyl ferro cene (dmFc) modified paste electrodes are reported based on cyclic vol tammetry and amperometric measurements. The studies have been conducte d on the graphite paste electrodes,of different composition mainly; i) graphite and mediators (TCNQ/TTF/dmFc) paste only, ii) graphite, gluc ose oxidase and mediators (TCNQ/TTF/dmFc) modified paste, and iii) gra phite, mediators (TCNQ/TTF/dmFc) and peroxidase modified paste. The re sults 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 NADN has been studied on system i, whereas mediated elect rochemical oxidation of glucose has been studied on system ii. The res ults suggest that TCNQ is a better mediator for probing NADH and gluco se oxidase catalyzed reactions. The mediated electrochemical probing o f peroxide has been studied on the system iii. The results suggest tha t TTF is better mediator for probing peroxidase catalyzed reaction. Th e selectivity of the mediated electrochemical response of systems ii a nd iii has been studied based on the amperometric and voltammetric mea surements of glucose and peroxide on systems ii and iii followed by th e addition of ascorbic acid. The results show that mediated electroche mical responses of these systems at both anodic and cathodic potential s 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 nonmediated electrochemica l oxidation of ascorbic acid. The ascorbic acid is oxidized through di e mediated mechanism at the anodic potential of the mediators and is d irectly 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 detectio n of glucose in the presence of ascorbic acid.