Voltammetric detection of chlorogenic acid by Poly(3,4-ethylene-dioxythiophene) electrodes

This work aims at developing selective detection of chlorogenic acid (CGA), a critical phenolic acid related to the antioxidant level and taste of coffee, by a pristine poly(3,4-ethylenedioxythiophene) (PEDOT) electrode. The electrochemical oxidation of CGA on two types of PEDOT films, electrodeposited in aqueous (water, aq-PEDOT) and non-aqueous solvents (acetonitrile, ACN-PEDOT), were systematically studied and compared. Aq-PEDOT film showed a linear response for CGA in a range from 1.5 µM to 2.5 mM and a sensitivity of 0.33 mA/cm²⋅mM; ACN-PEDOT film showed a non-linear response with residual CGA. For repeated sensing purposes, we chose aq-PEDOT for the CGA sensor demonstration. Although cross-sensitivity with gallic acid (GA) and caffeic acid (CA) at 0.35 V was observed due to the shared catechol structure, selectivity for CGA determination against vanillin (VAN), guaiacol (GUA), theobromine (THB), theophylline (THP), quinic acid (QA), and caffeine (CAF) was confirmed. The distinct sensing behavior of the PEDOT films was further investigated: aq-PEDOT had a relatively flat surface and obeyed diffusion-controlled kinetics for CGA electro-oxidation. In contrast, ACN-PEDOT had a rougher coral-like morphology and strong adsorption characteristics. The measurements in real coffee samples by aq-PEDOT were also demonstrated with the interference from CA compensated. In brief, this study proves the niches and provides in-depth electrochemical kinetics for voltammetric CGA sensing using the PEDOT films prepared in aqueous and non-aqueous environments.