A label-free photoelectrochemical biosensor with ultra-low-background noise for lead ion assay based on the Cu

Herein, a label-free and ultra-low-background-noise PEC biosensor was developed for lead ion (Pb2+) assay based on the Cu2O-CuO-TiO2 heterojunction. By calcination of cupric ion (Cu2+) doped-titanium based metal organic framework (MOF) material (NH2-MIL-125), the Cu2O-CuO-TiO2 heterojunction was synthesized. With Pb2+, lots of DNA single strands (S1) could be released based on the Pb2+ assisted cyclic amplification strategy and hybridized with hairpin DNA (HP1) on the modified electrode. The exposed phosphate groups on S1 can adsorb Cu2O-CuO-TiO2 heterojunction, which results in a large cathode photocurrent. Due to the good photoelectric property of Cu2O-CuO-TiO2 and Pb2+-triggering cyclic amplification strategy, the constructed PEC biosensor achieves a wide linear detection range (10 fM - 1 μM) and a low detection limit (6.8 fM), which provides potential applications in ultrasensitive determination of Pb2+ in environmental water samples and organisms.