A colorimetric and fluorescence dual-detection study of total antioxidant capacity in foods using iron-doped carbon dots

Nanozymes are artificial enzymes exhibiting significantly superior enzymatic activity compared to natural enzymes, and they are widely applied in the field of sensors. Carbon quantum dots (CDs) can serve as nanozymes, but their enzymatic activity is relatively low. To address this issue, this study incorporated iron atoms into carbon quantum dots to synthesize Fe-CDs, which demonstrated peroxidase (POD)-like enzyme catalytic activity and blue fluorescence. The POD enzyme activity of Fe-CDs is attributed to the Fenton reaction occurring between hydrogen peroxide and iron ions, which generates hydroxyl radicals with potent oxidative properties. In the presence of H 2 O 2 , Fe-CDs oxidize the colorless 3,3’,5,5’-tetramethylbenzidine (TMB) to blue ox-TMB. Subsequently, the system’s fluorescence was quenched via the internal filter effect (IFE). As is well known, L-Ascorbic acid (AA) exhibits strong reducing properties, reducing blue ox-TMB to colorless TMB while restoring fluorescence. This process exhibits a linear relationship. Based on the aforementioned strategy, a dual-mode sensing platform employing colorimetric and fluorescence detection for ascorbic acid with a linear range of 1-80 µM, and detection limits of 0.33 and 0.23 µM, respectively. Furthermore, a portable method for detecting AA was established using a mobile phone’s camera and colorimetry function. Fe-CDs can also realize convenient and rapid determination of total antioxidant capacity (TAC) in fruit juices, exhibiting outstanding enzymatic activity and specificity, which endow them with promising application prospects in the food industry.