Sn-Triggered Protein Self-Assembly Photoanode Based on CdS Quantum Dots and Au Nanoparticles for Dual-Electrode Photoelectrochemical Detection of Pb²⁺

Protein self-assembly has attracted extensive interest in the field of biomaterials and biomedicine due to its inherent biocompatibility and flexible designability. In this paper, we propose a potential route to generate a photoelectrochemical (PEC) sensing platform through Sn-triggered protein self-assembly. Specifically, Sn2+ ion was used to trigger the self-assembly of bovine serum albumin (BSA) to form in situ Sn/BSA film on the indium tin oxide (ITO) glass. Then, a CdS thin film as a PEC active material was electrodeposited on the Sn/BSA modified ITO electrode. The hybrid Sn/BSA film was demonstrated to stabilize the PEC response of the CdS. A dual-electrode PEC cell comprised a graphene oxide (GO)-modified photocathode and a Sn/BSA hybrid film/CdS-loaded photoanode. Pb2+-response deoxyribozymes (DNAzymes) were hybridized with the substrate strands tagged with Au nanoparticles (Au NPs) and then immobilized on the photocathode. Upon Pb2+-induced cleavage, Au NP-linked oligonucleotide fragment dislocated from the photocathode surface, resulting in a decrease in the PEC response. The present PEC biosensor showed highly sensitive detection of Pb2+ with a wide detection range from 10.0 fM to 0.1 μM and a low detection limit of 4.0 fM. This work demonstrates that the Sn/BSA hybrid film has potential application prospects in PEC sensing, thereby providing a new way of thinking for the design and development of the bioinspired biosensor.