A novel visible-light driven photoelectrochemical immunosensor based on multi-amplification strategy for ultrasensitive detection of microcystin-LR.

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.