Wiring Xanthine Oxidase Using an Osmium-Complex-Modified Polymer for Application in Biosensing.

Abstract

Xanthine is a metabolite of interest as a medical and food freshness biomarker. We modified a screen-printed electrode to detect this analyte by co-entrapping xanthine oxidase (XOD) and an Os-complex redox polymer over carbon nanotubes. In nature, XOD transfers its electrons to oxygen in solution. We demonstrate that the introduction of the redox polymer allows routing the electrons efficiently to the electrode surface, even under air-saturated conditions, enabling superior catalytic current and sensing performance. The bioanode was optimized by adjusting the electrode materials and the ratio of enzyme to redox polymer. The impacts of pH and ionic strength of the electrolyte on the sensor performance were also studied. We found that these variables can affect the electrostatic interaction between the enzyme and the redox polymer, and therefore impact the catalytic current extracted from xanthine oxidation. The XOD-bioanode design was combined with a bi-enzymatic cathode operating on glucose to demonstrate a biofuel cell (BFC). The resulting device could generate a power output of 16.56 μW cm−2 at 0.25 V and an open-circuit voltage (OCV) of 0.50 V using 500 μM xanthine as biofuel. The proposed xanthine/glucose BFC showed promising features for application as a self-powered xanthine biosensor.