Photoelectrochemical immunoassay of cardiac troponin I based on ZnTCPP/CdIn 2 S 4 type-II heterojunction and co-catalyzed precipitation biolabeling.

CdIn 2 S 4 and zinc tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) were synthesized by hydrothermal method, and an organic dye-sensitized inorganic semiconductor ZnTCPP/CdIn 2 S 4 type II heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode. A sandwich immunostructure for signal-attenuation photoelectrochemical (PEC) detection of cardiac troponin I (cTnI) was constructed using the ZnTCPP/CdIn 2 S 4 /FTO photoanode and a horseradish peroxidase (HRP)-ZnFe 2 O 4 -Ab 2 -bovine serum albumin (BSA) immunolabeling complex. The bioenzyme HRP and the HRP-like nanozyme ZnFe 2 O 4 can co-catalyze the oxidation of 4-chloro-1-naphthol (4-CN) by H 2 O 2 to produce an insoluble precipitate on the photoanode, thus notably reducing the anodic photocurrent for quantitative determination of cTnI. Under the optimal conditions, the photocurrent at 0 V vs. SCE in 0.1 M phosphate buffer solution (pH 7.40) containing 0.1 M ascorbic acid was linear with the logarithm of cTnI concentration from 500 fg mL -1 to 50.0 ng mL -1 , and the limit of detection (LOD, S/N = 3) is 0.15 pg mL -1 . Spiked recoveries were 95.1% ~ 104% for assay of cTnI in human serum samples.