A comparative study on electrochemical synthesis of carboxylic acid substituted indoles and their application in selective oxidation of dopamine

A comparative study on electropolymerization of 2, 3, 5 and 6-carboxylic acid substituted derivatives of indole over glassy carbon electrode (GCE) is reported. Electropolymerization ocurred in case of 2, 5 and 6-substituted indoles. Among these, the polymers resulting from 5 and 6-substituted derivatives are found soluble in aqueous medium and characterized by cyclic voltammetry, UV-vis spectroscopy and visual photographs. The processable polymers are cast over GCE using Nafion^® and used for selective sensing of Dopamine (DA) in presence of Ascorbic acid (AA). When such polymer matrix is coupled with redox mediators viz. tetracyanoquinodimethane (TCNQ), ferrocene (Fc) and dimethyl ferrocene (dmFc), differential amplified responses in each case on DA sensing are recorded. The sensitivity of DA analysis over these electrodes are found to be 18 ¿A ± 6 nA/mM, 14 ¿A ± 11 nA/mM¿and 16 ¿A ± 9 nA/mM¿ for TCNQ, Fc and dmFc respectively whereas the lowest detection limit is found to be 4 ¿M in each case.