Iron-doped carbon dots with multi-enzyme activities for rapid determination of phenolic compounds

Multi-enzymic nanozymes have attracted growing attention due to their distinct advantages over single enzyme-like nanozymes, particularly their synergistic effects and cascaded reactions. Herein, iron-doped carbon dots (FeCDs) were prepared by a one-step calcination method using hemin chloride, histidine, and potassium citrate as precursors. The resultant FeCDs exhibit a monodispersed spherical structure with an average particle size of 1.1 nm, where iron acts as a key catalytic active center. Enzyme activity experiments demonstrate that FeCDs exhibit peroxidase-like, catalase-like, and photo-enhanced laccase-like activities. Through the cascade effect of catalase-like and laccase-like activities of FeCDs, the coupling rate of 2,4-dichlorophenol (2,4-DP) and 4-amino-antipyrine (4-AP) was significantly increased. Meanwhile, the peroxidase-like activity can catalyze H₂O₂ to form ˙OH, further increasing the oxidation rate of 2,4-DP. Kinetic experiments indicated that the K_cat/K_m value of the combined action of the three enzyme-like activities was 3.35 times that of the peroxidase-like activity and 4.76 times that of the laccase-like activity, respectively. Based on the multi-enzyme activities of FeCDs, a series of phenolic compounds can be catalytically transformed into chromogenic products within 10 min at room temperature for the rapid determination of these compounds. The results obtained in this work not only provide a reliable strategy for the preparation of carbon-based nanomaterials with multi-enzyme activities, but also expand the application of carbon-based nanomaterials in the field of analysis.