A novel multi-amplification photoelectrochemical immunoassay based on copper(II) enhanced polythiophene sensitized graphitic carbon nitride nanosheet

A new sandwich photoelectrochemical (PEC) sensing strategy was proposed for the first time based on the increasing photocurrent of water-soluble polythiophene sensitized g-C3N4 nanosheet (PT-Cl/g-C3N4) in the presence of copper(II) (Cu2+), which was doped on the surface of titanium dioxide as labels for multi-amplification. Herein, the photoactive films of PT-Cl/g-C3N4 is employed as the photoactive antibody (Ab1) immobilization matrix for the subsequent sandwich-type antibody-antigen affinity interactions. Upon the presence of antigen (Ag), greatly enhanced photocurrent could be triggered in the PEC platform by the labels of second antibody (Ab2) of Cu2+ doped titanium dioxide (Cu2+-TiO2). As a result of the multi-amplification in this Cu2+-TiO2 enhanced PT-Cl/g-C3N4-based PEC immunoassay, it possesses excellent analytical performance. The antigen could be detected from 0.01 pg mL−1 to 100.0 ng mL−1 with a detection limit of 5 fg mL−1. This work opens up g-C3N4 nanosheet applied in PEC sensing. More importantly, the strategy of specific positive effect of Cu2+ on the photocurrent of g-C3N4 opens an alternative horizon for PEC sensing.