Amperometric biosensor for hypoxanthine based on immobilized xanthine oxidase on nanocrystal gold–carbon paste electrodes

The preparation and performance of a xanthine oxidase (XOD) biosensor, based on a carbon paste electrode (CPE) modified with electrodeposited gold nanoparticles (nAu), for the amperometric determination of hypoxanthine (Hx) is reported. Different XOD biosensor configurations were evaluated and compared with electrodes constructed by immobilizing XOD onto unmodified CPE and with biosensors prepared using glassy carbon electrodes and gold disk electrodes modified with electrodeposited gold. The XOD–nAu–CPE in which the enzyme was immobilized by cross-linking with glutaraldehyde (GA) and BSA exhibited the highest amperometric signal for Hx. Although Hx detection is usually carried out at potential values of around +600 mV versus Ag/AgCl, the GA–BSA–XOD–nAu–CPE allowed this detection to be carried out at 0.00 V, thus minimizing potential interferences from electrochemically oxidizable substances such as ascorbic acid. Experimental variables concerning the biosensor preparation were optimized. Calibration plots for Hx were constructed with the biosensor operating at +600 mV and at 0.00 V. The detection limit for Hx, 2.2 × 10−7 mol l−1, obtained using the latter potential value is similar to the best detection limits reported in the literature with other biosensor designs working at much more extreme potentials. The usefulness of the biosensor for the analysis of real samples was demonstrated by determining Hx in sardines and chicken meat.