Supporting Information for "Development of a Molecular Recognition Electrode and Investigation of a Biomolecular Application in Non-Aqueous Media -Electrochemical Detection of Uremia-Related Substances Excreted via ATP-Binding Cassette Transporter G2-"

Detection methods for small biological molecules are needed to facilitate analysis of physiological and pathological mechanisms. We aimed to construct a 2-mercaptobenzimidazole modified gold nanoparticle electrode for detection of uremia-related substances, e.g. uric acid (UA) and indoxyl sulfate (IS), excreted via transporters expressed on cultured cells. This electrode detected the current changes in phosphate buffer at different potentials as the concentrations of ascorbic acid, UA, dopamine, and IS were linearly increased in 1 µg/mL increments. Real-time detection of IS excretion via ATP-binding cassette transporter G2 (ABCG2) expression was performed in a transcellular transport model with amperometric measurement. The electrode was highly sensitive to the current changes with IS even in a serum-free culture medium. We observed an increase in current of approximately 0.10 µA per mm² of polycrystalline electrode surface area with each 1 µg/mL increase in IS concentration. The current increased with time when the electrode was exposed to cells transfected with ABCG2 plasmid in tissue culture insert, indicating that IS excretion occurred via the transporter encoded by ABCG2. In conclusion, the electrode could be successfully used for the real-time detection of IS excreted via ABCG2 expressed on cultured cells.