Biomass-Derived Carbon Dots-Based FRAP Analog for Sensitive Evaluation of Antioxidant Activity: Application to...

Ferric reducing antioxidant power (FRAP) is a well-established antioxidant in vitro assay. This work introduces an innovative FRAP-analog assay based on green-synthesized carbon dots (GCDs) for the sensitive evaluation of antioxidant activity. The GCDs were prepared via ordinary roasting of sweet potato, which is considered a natural and renewable precursor, yielding highly fluorescent (quantum yield 53%), water-soluble CDs with excellent ferric (Fe³⁺) complexing activity. In this system, the addition of Fe³⁺ leads to quenching of the fluorescence of GCDs. Antioxidant-induced reduction of Fe³⁺ to Fe²⁺ leads to a measurable turn on effect. Using ascorbic acid as a reference antioxidant, the sensor exhibited a linear response between 2 and 14 μg/mL (R² 0.996) with a limit of detection of 0.82 μg/mL, very good accuracy (recovery = 103.27% ± 3.48%) and acceptable precision (RSD = 1.01%-5.61%). The developed assay was applied successfully to pharmaceutical products and plant extracts. The GCD-based FRAP analog demonstrated strong correlation with traditional FRAP assays. The devised approach eliminated the use of toxic nonrenewable reagents, rendering it excellent green on both analytical Eco-scale, Analytical GREEnness (AGREE), and Nano Eco-Scale metrics. This green, nanomaterial-based approach provides a promising alternative for antioxidants' analysis in food and pharmaceuticals.