Hemin-assisted synthesis of peroxidase-like Fe-N-C nanozymes for detection of ascorbic acid-generating bio-enzymes

Revealing the relationship between composition and enzyme-like activities is essential for the rational designs of nanozymes and related assays with improved performances. Here, a series of Fe-N co-doped porous carbon (Fe-N-C) nanozymes containing different Fe contents have been successfully prepared by facilely pyrolyzing hemin trapped zeolitic-imidazolate-frameworks (Hemin@ZIF-8). The special doping agent hemin will endow Fe-N-C with exceptionally high peroxidase-mimetic activities due to the hierarchically porous structure, high specific surface area, and high dispersed Fe-N_x sites. Notably, the optimal Fe₅₅-N-C nanozymes are used to detect bio-enzymes, by taking alkaline phosphatase (ALP) as a model, based on the inhibition of nanozymatic activity by ascorbic acid (AA). A linear activity range of 0.05-20 U/L is obtained with a low detection limit of 0.03 U/L, which is superior to the most published optical ALP assays. This work provides not only a new method for the design of the transition metal-N-C nanozyme with enhanced peroxidase-like activity but also a promising strategy for the detection of ascorbic acid-generating bio-enzymes with the assistance of specific substrates.