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.