A signal-off sandwich photoelectrochemical immunosensor using TiO2 coupled with CdS as the photoactive matrix and copper (II) ion as inhibitor

•This photoelectrochemical bioassay is based on the signal-off strategy of Cu2+.•CuO, as the labels of antibody, is first applied in the photoelectrochemical biosensor.•The polythiophene is introduced to make the biosensor more stable.•This photoelectrochemical biosensor shows good stability, sensitivity and selectivity.

In this work, a novel sandwich photoelectrochemical (PEC) biosensor was developed based on a signal-off strategy using TiO2 coupled with CdS quantum dots (QDs) as the photoactive matrix and copper (II) ion (Cu2+) as inhibitor. TiO2/CdS modified indium tin oxide (ITO) electrode was employed for primary antibody (Ab1) immobilization and the subsequent sandwich-type antibody–antigen (Ab–Ag) affinity interactions. Flower-like copper oxide (CuO) was used as labels of secondary antibody (Ab2) and immobilized on the modified electrode via specific affinity interactions between Ab2 and Ag. Cu2+ was released by dissolving CuO with HCl, and then reacted with CdS to form CuxS (x=1, 2), which would create new energy levels for electron–hole recombination and resulted in a decrease of the photocurrent. CuO, as the labels of Ab2, was first applied in PEC biosensor based on the signal-off strategy of the Cu2+ for CdS. Greatly enhanced sensitivity was achieved through the coupling of CdS QDs with TiO2. Besides, the introduction of polythiophene (PT-Cl) on the surface of TiO2 made the PEC signal more stable. Under 405 nm irradiation at 0.1 V, the PEC biosensor for H–IgG determination exhibited a linear range from 0.1 pg mL−1 to 100 ng mL−1 with a low detection limit of 0.03 pg mL−1. The proposed biosensor showed high sensitivity, stability and selectivity, which opens up a new promising signal-off PEC platform for future bioassay.