A novel visible-light driven photoelectrochemical immunosensor based on multi-amplification strategy for...

An ultrasensitive photoelectrochemical (PEC) immunoassay based on multiple signal amplification strategy was fabricated for the detection of microcystin-LR (MC-LR). The CdS/TiO₂ nanorod arrays (CdS/TiO₂ NRAs) modified FTO electrode, which can weaken the self-oxidation by photogenerated holes of CdS nanoparticles, and limit the recombination of electron-hole pairs and broaden optical absorption of TiO₂ NRAs, was used as a visible-light driven material to immobilize antigens. Then, Fe₃O₄ nanoparticles/polydopamine (Fe₃O₄@PDA) was used as the carrier to load secondary antibody (Ab₂) and horseradish peroxidase (HRP), where Fe₃O₄ nanoparticles and HRP can synergistically accelerate the oxidation of 4-chloro-1-naphthol (4-CN) by H₂O₂ to produce biocatalytic precipitation (BCP) on the surface of modified electrode. Due to the catalytic activity of Fe₃O₄ nanoparticles and HRP, the nonproductive absorption of HRP and the steric hindrance by BCP, the photocurrent change was amplified. The proposed PEC immunosensor can detect MC-LR in a range of 0.005-500 μg/L with a detection limit of 0.001 μg/L. Meanwhile, the PEC immunosensor exhibited high sensitivity, good stability, acceptable selectivity and reproducibility, indicating its potential application in environmental monitoring.