High-activity FeO nanozyme as signal amplifier: A simple, low-cost but efficient strategy for ultrasensitive photoelectrochemical immunoassay.

Sensitive but with simple, inexpensive detection of disease-related biomarkers in real biological samples is of quite necessity for early diagnosis and disease surveillance. We herein first introduced high-activity FeO nanozyme as signal amplifier to develop an ultrasensitive photoelectrochemical (PEC) immunoassay, which meanwhile has the distinct merits of both simplicity and low cost compared with previously reported enzyme-labeling PEC immunoassays. In the proposal, to illustrate and describe the PEC platform, prostate-specific antigen (PSA, Ag) was used as a target model. Specifically, ZnO nanorods (ZnO-NRs) grown vertically on a bare indium-tin oxide (ITO) electrode was deposited with ZnInS nanocrystals, producing ZnInS/ZnO-NRs/ITO photoelectrode as the PEC matrix to modify capture PSA antibody (Ab). Histidine-modified FeO (his-FeO) nanozyme as signal amplifier was linked with signal PSA antibody (Ab) to form his-FeO@Ab conjugate, and was anchored through specific sandwich immunoreaction. The labeling his-FeO nanozyme acted as a peroxidase to induce the generation of the insoluble and insulating precipitation, resulting in an evident decrease in the photocurrent signal. On account of combined effects of high catalytic efficiency of the his-FeO nanozyme and excellent PEC properties of the ZnInS/ZnO-NRs/ITO photoelectrode, ultralow detection limit of 18 fg/mL for target Ag detection was achieved. Besides, as high-activity his-FeO nanozyme has substituted natural enzyme as signal amplifier, simplicity and low cost of the PEC immunoassay was realized.