Photoelectrochemical competitive immunosensor for 17β-estradiol detection based on ZnIn2S4@NH2-MIL-125(Ti) amplified by PDA NS/Mn: ZnCdS

A competitive-type PEC immunosensor for 17 beta-estradiol (E-2) detection was successfully fabricated using ZnIn2S4@NH2-MIL-125(Ti) composite as matrix. The excellent PEC behavior of ZnIn2S4@NH2-MIL-125(Ti) composite could be attributed to that the Ti4+-Ti3+ intervalence cycles in the titanium oxo-cluster of NH2-MIL-125(Ti) as well as the matching energy level between ZnIn2S4 and NH2-MIL-125(Ti) promote the migration and separation of photocarrier. Besides, polydopamine (PDA) with abundant amino- and quinone-groups was selected to further improve the PEC signals and capture antibody, which implement through the covalent bonding of PDA and BSA-E-2 or carboxyl-group functionalized Mn:ZnCdS QDs in the competitive-type strategy. Concretely, the quinone functional groups in PDA film was applied to immobilize BSA-E-2 through Michael reactions, and the PDA nanosphere loaded Mn:ZnCdS quantum dot (PDA NS/Mn:ZnCdS QDs) was used as antibodies' labels to amplify PEC signals. After PDA NS/Mn:ZnCdS-anti-E-2 immobilized on the modified electrode, a remarkable increase of photocurrent signal was observed owing to the specific bonding of antigen and antibody. Based on the competitive binding of PDA NS/Mn:ZnCdS-anti-E-2 with either free E-2 or bovine serum albumin (BSA)-E-2 causing the change of the photocurrent signal, the standard sample free E-2 could be accuracy detect. Under optimal conditions, the competitive-type PEC immunosensor exhibited the linear range from 0.0005 ng/mL to 20 ng/mL and a limit detection of 0.3 pg/mL (S/N = 3). Meanwhile, the acceptable stability, selectivity and reproducibility of the proposed PEC immunosensing platform indicating the promising detection of small molecular environmental pollutants.