Three-Channel Electron Engineered Fe-88A@CeO2/CDs Nanozyme with Enhanced Oxidase-Like Activity for Efficient Biomimetic Catalysis.

Iron-based metal-organic framework (MOF) nanozymes have garnered considerable attention owing to a large specific surface area, adjustable porosity, large Fe-O clusters, and unsaturated Fe sites. However, the sluggish charge-transfer rate and restricted active sites of the nanozymes lead to poor enzyme-like activity and further impede their biomimetic catalysis. Herein, a three-channel electron-engineered Fe-88A@CeO2/carbon dots (Fe-88A@CeO2/CDs) nanozyme is proposed for efficient biomimetic catalysis. Fe-88A@CeO2/CDs nanozyme is prepared by incorporation of CeO2 and CDs into the porosity of Fe-88A. Specifically, the original Fe (II)/Fe (III) and the introduced Ce (III)/Ce (IV) redox couples of the nanozyme constitute a dual electron transfer channel. Furthermore, the presence of CDs produces another electron transfer channel. The three-channel electron engineering strategy for nanozymes can accelerate the electron transfer process accompanied with more active sites, thereby greatly enhancing the oxidase-like activity of Fe-88A@CeO2/CDs for biomimetic catalysis. The nanozyme can efficiently convert oxygen to · O 2 - ${\mathrm{O}}_2^ - $ , oxidizing colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB, and meanwhile the ox-TMB effectively quenches the fluorescence of CDs. As proof of concept, the nanozyme is utilized to construct a colorimetric-fluorescence bimodal immunosensor for monitoring Staphylococcal enterotoxin B with excellent performance. This work provides promising insight into designing excellent nanozymes for effective biomimetic catalysis in various fields.