Electrochemical detection of choline via oxygen consumption in a thermally reduced graphene oxide matrix: Advantages of operation at both positive and negative potentials

An amperometric choline biosensor was developed using synthesised thermally reduced graphene oxide (TRGO) as an efficient electrochemical surface and immobilisation matrix for choline oxidase (ChOx). The biosensor can operate via two distinct mechanisms depending on the applied working electrode potential: dissolved oxygen (O₂) consumption at −0.3 V and hydrogen peroxide oxidation at +0.6 V vs Ag/AgCl. Under these conditions, the TRGO/ChOx biosensor exhibited a linear response to choline concentrations of 0.0009–0.24 mM and 0.0008–0.24 mM, with sensitivities of 29 and 38 μA mM −1 cm −2 at −0.3 V and + 0.6 V vs Ag/AgCl, respectively. Operation at −0.3 V significantly improved biosensor selectivity by minimizing interference from common biological species, including dopamine, adenosine, serotonin, uric acid, ascorbic acid, glucose, albumin, and epinephrine. The TRGO/ChOx biosensor demonstrated excellent accuracy in mouse urine samples, yielding recovery rates of 101–107 % and relative standard deviations of 0.4–3.9 %. These features, including the dual operating mechanisms, highlight the strong potential of this biosensor for rapid and reliable choline detection in non-invasive diagnostics. • TRGO enhanced the bioelectrocatalytic activity of choline oxidase. • Dual-mode choline detection via O₂ consumption and H₂O₂ oxidation. • Wide linear range with high sensitivities at both positive and negative potentials. • Potential for rapid and reliable detection of choline in non-invasive analysis.