Highly sensitive electrocatalytic biosensing of hypoxanthine based on functionalization of graphene sheets with water-soluble conducting graft copolymer

A novel electrocatalytic biosensing platform was designed by the functionalization of reduced graphene oxide sheets (RGO) with conducting polypyrrole graft copolymer, poly(styrenesulfonic acid-g-pyrrole) (PSSA-g-PPY), via π–π noncovalent interaction. The resulting nanocomposite could well disperse in water for at least 2 months with a solubility of 3.0 mg mL−1. The nanocomposite was characterized with atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible absorption, contact angle measurement, and electrochemical impedance spectroscopy. Based on the advantageous functions of PSSA-g-PPY and RGO, the functional nanocomposite modified platinum electrode showed high electrocatalytic activity toward the oxidation of hydrogen peroxide and uric acid in neutral media. Further, a hypoxanthine biosensor was constructed by combining the modified electrode with the enzymatic reaction of xanthine oxidase. The biosensor exhibited a wide linear response ranging from 3.0 × 10−8 to 2.8 × 10−5 M with a high sensitivity of 673 ± 4 μA M−1 cm−2. The detection limit of 10 nM at a signal-to-noise ratio of 3 was one order of magnitude lower than that reported previously. The assay results of hypoxanthine in fish samples were in a good agreement with the reference values. The water-soluble conducting copolymer could serve as an efficient species for functionalization and solubilization of graphene sheets in biosensing and biocatalytic applications.