Coffee grounds-derived carbon quantum dots as peroxidase mimetics for colorimetric and fluorometric detection of ascorbic acid

Abstract

In this study, we reported the eco-responsible synthesis of iron-doped carbon quantum dots (Fe-CQDs) from waste coffee grounds through a simple hydrothermal method. The Fe-CQDs exhibited high peroxidase-like activity, which could convert 3,3',5,5'-tetramethylbenzidine (TMB) into blue ox-TMB in the presence of H₂O₂. After adding ascorbic acid (AA) to above system, the blue solution faded. Based on this phenomenon, a colorimetric method for visual monitoring of H₂O₂ and AA was developed. Meanwhile, the fluorescence of Fe-CQDs can be quenched by the formed ox-TMB via inner filter effect (IFE), followed by the recovery upon the addition of AA. Therefore, Fe-CQDs can be acted as a fluorescent probe to detect H₂O₂ and AA through the "on-off-on" mode. Furthermore, the dual-recognition methods based on Fe-CQDs were used to measure AA content in beverage samples. Thus, this work would shed much light on converting waste into biomass CQDs and their potential applications in biomolecular detection.

Keywords: Ascorbic acid; Carbon quantum dots; Coffee grounds; Dual-recognition; Peroxidase-like activity.