Amperometric biosensors based on reduced GO and MWCNTs composite for polyphenols detection in fruit juices

Amperometric biosensors based on glassy carbon electrodes (GCE) modified with graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) were developed. Two types of biosensors were realized employing tyrosinase (Tyr) or laccase (Lac). Before enzyme deposition GO was reduced by electrochemical route performing cyclic voltammetry. The enzyme immobilisation on the modified GC was optimised employing different agents (bovine serum albumin and glutaraldehyde as crosslinking agent, chitosan, and Nafion). The conditions for the fabrication and the storage of the biosensors were established in order to obtain good enzyme retention, high sensitivities and long-life devices. The biosensors were used for the determination of catechol and other polyphenols, i.e., pyrogallol, epicatechin, gallic acid, 1,2-dihydroxybenzoic acid, caffeic acid, chlorogenic acid, rutin, catechin and dopamine. Eventually, their practical applicability was demonstrated by estimating the total polyphenols concentration in juice samples, expressed as epicatechin equivalents.