A label-free photoelectrochemical biosensor for urokinase-type plasminogen activator detection based on a g-C3N4/CdS nanocomposite

Highlights: • A novel, lable-free photoelectrochemical biosensor was constructed for urokinase-type plasminogen activator (u-PA) detection. • Urokinase-type plasminogen activator (u-PA) was first time detected by photoelectrochemical technique. • The proposed photoelectrochemical protocol presented ultrahigh sensitivity, reproducibility, specificity and stability. - Abstract: Herein, we established a novel ultrasensitive photoelectrochemical biosensor for detecting urokinase-type plasminogen activator (u-PA), based on a g-C₃N₄/CdS nanocomposite. The prepared nanocomposite was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible absorption spectroscopy, and Fourier transform infrared spectroscopy, thus indicating that the nanocomposite was prepared successfully. In the typical process, the prepared nanocomposite was deposited on the surface of a bare FTO electrode. After being air-dried, the g-C₃N₄/CdS nanocomposite modified electrode was successively incubated with antibody against urokinase-type plasminogen activator and the blocking agent BSA to produce a photoelectrochemical biosensor for u-PA. In the presence of target u-PA antigen, the photocurrent response of the prepared biosensor electrode decreased significantly. The proposed novel photoelectrochemical biosensor exhibited good sensitivity, specificity, and reproducibility for u-PA detection, and a low detection limit of 33 fg mL^-1, ranging from 1 µg mL^-1–0.1 pg mL^-1. The proposed strategy should provide a promising method for detection of other biomarkers.