Development of a highly sensitive xanthine oxidase-based biosensor for the determination of antioxidant capacity in Amazonian fruit samples.

The paper describes the development of an amperometric biosensor using Prussian Blue (PB) modified electrodes containing xanthine oxidase (XOD). The enzyme is immobilized by photo-polymerization into an azide-unit pendant water-soluble photopolymer (PVA-AWP). The parameters of the fabrication of the biosensor, XOD:PVA/AWP ratio, crosslinking irradiation time, and XOD charge, were optimized. Operational conditions for electrode preparation were defined as 1:2 ratio of XOD:PVA/AWP; exposure time to neon light of 30  min; pH = 7.5  at room temperature and enzymatic charge of 8 mU per electrode. The biosensors showed stable, fast, simple, selective, cost-effective and sensitive (-2.72E-8  A mol L-1), with a good linear range (1.0-75  μmol L-1), and respectively detection and quantification limits for antioxidants of 2.17, and 7.15  μmol L-1. The applicability of this biosensor was demonstrated by in vitro analysis of gallic acid as standard antioxidant and Amazonian fruits as natural sources.