Electrochemical biosensor based on singlet oxygen generated by molecular photosensitizers.

Here a sensing strategy with the integration of photosensitizer and electrochemical analysis was present. The photosensitizer, Zinc(II) tetraphenylporphyrin (ZnTCPP), was functionalized graphene oxide (GO) to form complex (ZnTCPP/GO) as the electrode material and generated singlet-oxygen (1O2) in the presence of air under light illumination. Due to the special electronic structure of 1O2, hydroquinone (HQ) could react with 1O2 to produce electrochemically-detectable products, benzoquinone (BQ). Meanwhile, the formed BQ could be reduced on the electrode, completing the redox cycling. The ZnTCPP/GO modified ITO electrode produces a stable and enhanced photocurrent signal under 420 nm irradiation in air-saturated buffer, compared with in N2-saturated buffer. On the other hand, l-glutathione (GSH) as a signalling molecule plays important role in physiological process, which was employed as model to investigated the sensing performance. Coupling with HQ oxidized by 1O2, a GSH sensor was constructed on the basis the redox cycling of HQ. A sensitive reduction of photocurrent is observed with the addition of GSH, due to the GSH could be oxidized by the generated 1O2 to form GSSG. The biosensor displayed good performance in a broad concentration range of 0-150 μM, with a lower detection limit of 1.3 μM at an S/N ratio of 3, and could be used in practical application. This work affords a platform for constructing the biosensor with 1O2 instead of enzyme via on/off light switching.