We report herein a new guanine sensor for the determination of guanine based on a photoelectrochemical effect of poly(thionine) photoelectrode to hydrogen peroxide (H₂O₂). The photoelectrode was fabricated by electropolymerizing thionine on the surface of ITO electrode. And then xanthine oxidase was immobilized on the photoelectrode via the aid of chitosan enwrapping, forming an enzyme-modified photoelectrode. The photoelectrode was employed as an electron acceptor, and H₂O₂ from the catalytic reaction of enzyme was employed as an electron donor, the guanine can be detected due to photoelectrochemical effect between photoelectrode and H₂O₂. In the paper, photoelectrochemical effects of photoelectrode to H₂O₂ and guanine were studied. Effects of bias voltage, illumination intensity and electrolyte pH on the photocurrent were investigated. The linear response of guanine concentrations ranged from 1.00～200 μmol/L was obtained with a detection limit of 0.55 μmol/L. The guanine sensor was successfully applied to detect the disorganization of DNA mediated by heating acid solution and active ingredient of aciclovir. The relative standard deviation (RSD) was less than 5.37% and the recovery was in the range of 96.8%～106% for the determination of samples. The preparation of the sensor and the detection of guanine have the advantages of economy and simpleness due to without peroxidase and deoxygenated.

Key words: guanine sensor, photoelectrochemistry, guanine, xanthine oxidase, herring sperm DNA, aci clovir