Bioelectrocatalytic and electrochemical cascade for phosphate sensing with up to 6 electrons per analyte molecule

Kopiec, G. and Starzec, K. and Kochana, J. and Kinnunen-Skidmore, T.P. and Schuhmann, W. and Campbell, W.H. and Ruff, A. and Plumeré, N.

Volume: 117 Pages: 501-507
DOI: 10.1016/j.bios.2018.06.047
Published: 2018

Despite the availability of numerous electroanalytical methods for phosphate quantification, practical implementation in point-of-use sensing remains virtually nonexistent because of interferences from sample matrices or from atmospheric O2. In this work, phosphate determination is achieved by the purine nucleoside phosphorylase (PNP) catalyzed reaction of inosine and phosphate to produce hypoxanthine which is subsequently oxidized by xanthine oxidase (XOx), first to xanthine and then to uric acid. Both PNP and XOx are integrated in a redox active Os-complex modified polymer, which not only acts as supporting matrix for the bienzymatic system but also shuttles electrons from the hypoxanthine oxidation reaction to the electrode. The bienzymatic cascade in this second generation phosphate biosensor selectively delivers four electrons for each phosphate molecule present. We introduced an additional electrochemical process involving uric acid oxidation at the underlying electrode. This further enhances the anodic current (signal amplification) by two additional electrons per analyte molecule which mitigates the influence of electrochemical interferences from the sample matrix. Moreover, while the XOx catalyzed reaction is sensitive to O2, the uric acid production and therefore the delivery of electrons through the subsequent electrochemical process are independent of the presence of O2. Consequently, the electrochemical process counterbalances the O2 interferences, especially at low phosphate concentrations. Importantly, the electrochemical uric acid oxidation specifically reports on phosphate concentration since it originates from the product of the bienzymatic reactions. These advantageous properties make this bioelectrochemical-electrochemical cascade particularly promising for point-of-use phosphate measurements. © 2018 Elsevier B.V.

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