Iron-doped carbon dots with peroxidase activity for colorimetric and fluorometric dual-signal detection of tannic acid

Given the indispensable role and diverse applications of tannic acid in the food industry, the development of an efficient, precise, and rapid detection and measurement technology for tannic acid is of paramount importance. In this research, we presented the fabrication of iron-incorporated carbon dots (Fe-CDs) through a single-step hydrothermal method, employing Schiff base-structured iron complexes (Fe-Salen) and citric acid (CA) as precursors. Leveraging the catalytic properties of Fe-CDs, we developed a strategy that integrates colorimetric and fluorescence dual signal detection techniques to detect tannic acid (TA). At the heart of this strategy is the peroxidase-like (POD-like) activity exhibited by Fe-CDs, which effectively catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) into its visually discernible blue oxidized form (ox-TMB), in the existence of hydrogen peroxide (H2O2). Upon the addition of TA, the blue solution undergoes discoloration, enabling colorimetric detection. Furthermore, the interaction between Fe-CDs, TMB, and H2O2 significantly quenches the luminescence of Fe-CDs, and the recovery of fluorescence upon the addition of TA introduces an additional dimension of fluorescence signal to the detection process. This dual-signal detection mode not only enhances the sensitivity and accuracy of the assay but also broadens the potential applications of Fe-CDs in fields such as biological analysis and food safety.