Matrix redox interference-free nanozyme-amplified detection of Hg2+ using thiol-modified phosphatase-mimetic nanoceria

Given heavy metals pose huge threats to ecological system and human health, it is significant to monitor them. With the favorable feature of catalytic signal amplification, redox-type nanozymes have been widely used to detect heavy metals. However, the presence of redox substances in samples can interfere with these catalytic reactions, impacting the accuracy and repeatability of detection. To avoid the situation, here we designed a non-redox nanozyme (3-mercaptopropionic acid modified nanoceria, MPA-CeO2) and developed a novel approach free from matrix redox interference to detect Hg2+. The well-dispersed MPA-CeO2 showed high and stable phosphatase-mimetic activity to catalyze the hydrolysis of colorless p-nitrophenyl phosphate (p-NPP) to yellow p-nitrophenol (p-NP). The addition of Hg2+ could bind specifically onto the MPA-CeO2 particles through S–Hg bond and cause the latter to aggregate, thereby suppressing the ability of MPA-CeO2 with shielded active surfaces to hydrolyze p-NPP. According to the simple principle, highly sensitive and specific colorimetric measurement of Hg2+ was achieved, and excellent reliability and practicability were demonstrated by real sample analysis. To our best knowledge, this study is the first one of detecting Hg2+ using phosphatase-mimicking nanozymes, and it will inspire the exploration of new analytical methods via designing non-redox nanozymes for various targets.