MoSe₂/CdSe Heterojunction Destruction by Cation Exchange for Photoelectrochemical Immunoassays with a...

Herein, a split-type immunoassay strategy instigated by cation exchange (CE) and changing the capacity of an electron donor in an electrolyte solution is optimized, namely, for differentiating the biological-specific binding assay and photoelectrochemical (PEC) analysis. MoSe₂/CdSe, a Z-scheme heterojunction with efficient visible light absorption and a low recombination of carriers, is used as a photoelectrode substrate. Silver ions (Ag⁺) as the initiator of CE are generated by the acidolysis of evenly loaded silver nanoparticles on mesoporous silica nanospheres (MSNs). The theoretical calculation and experimental results confirm that Ag⁺ replaces Cd²⁺ in CdSe and retains the crystal structure of MoSe₂. However, this behavior destroys the perfectly matched heterojunction structure and introduces defects, which led to the reduction of the photocurrent response. In addition, ascorbate oxidase in combination with MSNs can be used as a consumptive agent of the electron donor, which further improves the sensitivity and reliability of the sensor. As a proof of principle, neuron-specific enolase was applied to elucidate the potential application of the PEC immunoassay in clinical diagnosis, and the obtained linear range of the sensor was from 0.0001 to 100 ng/mL with a detection limit of 28 fg/mL (S/N = 3).