Poly(bromocresol green) and poly(bromocresol purple) films by electropolymerization in ternary deep eutectic solvent on gold nanoparticle/graphene quantum dot modified electrodes for the biosensing of glucose.

The triarylmethane dyes brilliant cresyl green (BCG) and brilliant cresyl purple (BCP) have been electropolymerized on glassy carbon electrodes (GCE) modified with gold nanoparticles (AuNP) and graphene quantum dots (GQD) dispersed in chitosan (AuNP+GQD)chitosan by potential cycling in a novel ternary deep eutectic solvent (tDES). The tDES was composed of choline chloride (ChCl) as the hydrogen bond acceptor plus acetic acid and ethylene glycol as hydrogen bond donors, with perchloric acid as a tDES acid dopant. GQDchitosan was synthesized by a simple and eco-friendly procedure using citric acid as the carbon source in chitosan solution with 1% v/v acetic acid. AuNP dispersed in citrate buffer were mixed with GQDchitosan in the proportion (70/30% v/v). The PBCG/(AuNP+GQD)chitosan/GCE and PBCP/(AuNP+GQD)chitosan/GCE modified electrodes were compared and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The morphology of the synthesized polymer films was examined by scanning electron microscopy. After immobilization of glucose oxidase (GOx), GOx/PBCG/(AuNP+GQD)chitosan/GCE and GOx/PBCP/(AuNP+GQD)chitosan/GCE biosensors were employed for the determination of glucose by amperometry at a potential of -0.2 V vs. Ag/AgCl. Linear concentration ranges were 10-200 µM for GOx/PBCG/(AuNP+GQD)chitosan/GCE and 10-140 µM for GOx/PBCP/(AuNP+GQD)chitosan/GCE, with corresponding limits of detection of 2.3 µM and 3.1 µM. The biosensor with PBCG film showed slightly better analytical parameters. The biosensors demonstrated good repeatability, reproducibility, stability, and selectivity and were successfully applied to wine samples with very good recoveries.