Carbon Dots/g-C3N4 Nanoheterostructures-Based Signal-Generation Tags for Photoelectrochemical Immunoassay of Cancer Biomarkers Coupling with Copper Nanoclusters

A class of 0-dimensional/2-dimensional (0D/2D) nanoheterostructures based on carbon quantum dots (CQDs) and graphitic carbon nitride (g-C3N4) was designed as the signal-generation tags for the sensitive photoelectrochemical (PEC) immunoassay of prostate-specific antigen (PSA) coupling with the copper nanoclusters (CuNCs). Combination of CQDs with g-C3N4 promoted the photoexcited electron/hole separation and largely increased the photocurrents of the nanoheterostructures. Initially, a sandwich-type immunoreaction was carried out on monoclonal anti-PSA antibody-coated microplate by using PSA aptamer linked with CuNCs as the tracer. Accompanying the immunocomplex, the carried CuNCs were dissolved under acidic conditions. The as-released copper ions from the CuNCs could be captured onto the CQDs/g-C3N4 nanoheterostructures via the amino-group on the CQD surface as well as the -NHx (x = 1, 2, 3) of g-C3N4 nanosheets. The strong coordination of the Lewis basic sites on the CQDs/g-C3N4 with Cu2+ decreased the photocurrent of the nanoheterostructures. Under optimal conditions, CQDs/g-C3N4 nanoheterostructures displayed good photocurrent responses for the detection of PSA within the dynamic linear range of 0.02-100 ng mL(-1) and a limit of detection (LOD) of 5.0 pg mL(-1). This method was also evaluated for quantitative screening of human PSA serum specimens by using the referenced electrochemiluminescent enzyme-linked immunoassay (ECL-ELIA) and gave good matched results between two methods. Additionally, this system was beneficial to explore the charge-separation and photoinduced electron transfer mechanism in the photoelectrochemical sensing protocols.