An immunosensor for sensitive photoelectrochemical detection of Staphylococcus aureus using ZnS-AgS/polydopamine as photoelectric material and CuO as peroxidase mimic tag.

We report here sensitive photoelectrochemical immunosensing of Staphylococcus aureus (S. aureus) using ZnS-AgS/polydopamine (PDA) as a novel photoelectric material and CuO as the peroxidase mimic tag. ZnS-AgS heterojunctions were prepared on indium tin oxide (ITO) via electrodeposition of ZnS nanoparticles, followed by silver ion exchange. To prepare a PDA/ZnS-AgS/ITO, the ZnS-AgS/ITO electrode was coated with PDA by self-polymerization of dopamine. The photocurrent of the PDA/ZnS-AgS/ITO is 1.55 times that of the ZnS-AgS/ITO and 7.87 times that of the ZnS/ITO, indicating a high-performance photoelectric material. A sandwiched-type photoelectrochemical immunosensor was constructed by using PDA/ZnS-AgS/ITO as the photoelectrode and CuO nanocubes as the labels. CuO nanocubes can serve as peroxidase mimic to generate catalytic precipitates on the immunoelectrodes, and both the CuO nanocubes and the generated precipitates can decrease the photocurrents of the immunoelectrodes, so a photoelectrochemical immunosensor for detecting S. aureus was constructed, showing a linear range between 10 and 10 CFU mL and a low detection limit of 2 CFU mL. Owing to the signal amplification of CuO labeling, the sensitivity of the CuO-labeled immunosensor is 4 times that of a label-free immunosensor for detecting S. aureus, and the detection limit (2 CFU mL) is lower than that of a label-free immunosensor (10 CFU mL). This work not only provides a new and efficient photoelectric material but also demonstrated an efficient signal-amplification strategy for photoelectrochemical biosensing.