Red-Emissive Carbon Dots Combined with Ferric Ions for Detection of Total Antioxidant Capacity in Food

In general, the total antioxidant capacity (TAC) in food is vital for evaluating the quality of antioxidant food and health monitoring. Most studies about the access of the TAC in food are mainly focused on typical colorimetric strategies. Herein, a simple and sensitive strategy for TAC in beverages and fruit has been proposed based on amino/hydroxyl-functionalized carbon dots (N2H4-CDs) and Fe3+. The fluorescence (FL) of N2H4-CDs at 650 nm can be effectively and selectively quenched via the formation of the nonfluorescence complex (Fe3+/N2H4-CDs). Moreover, the FL of N2H4-CDs is concentrated in the red region, which can eliminate the interference in complex biological environments. Interestingly, based on the theoretical calculations of density functional theory (DFT), we have confirmed that the surface amino and hydroxyl play an essential role in selective association with Fe3+, resulting in effective quenching. Moreover, because Fe3+ can be reduced by antioxidants to Fe2+, the quenched FL of N2H4-CDs can be restored in the presence of ascorbic acid (AA) and glutathione (GSH). Therefore, the typical antioxidants (AA) and especially certain thiol antioxidants (GSH) can also be analyzed by the proposed strategy. More importantly, we have proved that this strategy is successfully utilized for analyzing the TAC in beverages and fruit.