A highly sensitive photoelectrochemical sensor with polarity-switchable photocurrent for detection of trace hexavalent chromium

Signal quenching photoelectrochemical sensors have attracted extensive research interests due to outstanding performance and simplicity in realization. This work proposes a photoelectrochemical sensor with photocurrent polarity-switchable property for highly selective and sensitive detection of trace hexavalent chromium (Cr(VI)) ion. Layer-by-layer self-assembled graphene intercalation layer and drop-coated TiO₂ nanocrystalline film are successively deposited onto patterned Au/SiO₂/Si electrodes. By facilitating the photon-excited electron-hole pair separation, graphene significantly enhances the intensity and stability of the device photocurrent. Coupled with light-sensitive quercetin and its specific interaction with Cr(VI), such sensors can selectively switch the photocurrent polarity from anodic to cathodic with increasing Cr(VI) concentration, resulting in a large sensing range from 1.4 ppb to 2592.3 ppb, with a low detection limit of 0.44 ppb. Featured by the facile fabrication process, low-cost materials, good selectivity, and stable photocurrent output, this sensor shows promising potential applications to on-site environment monitoring.