Colorimetric determination of ascorbic acid based on carbon quantum dots as peroxidase mimetic enzyme

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm. Interestingly, the ox-TMB could be further reduced by ascorbic acid (AA) leading to fading of the blue color and an absorbance decrease. Thus, a convenient and sensitive colorimetric method for detection of AA using CQDs as peroxidase mimics was established. Several factors, such as acidity, temperature, incubating time, and TMB concentration, which might influence the response of the analysis signal, were optimized. The results showed that the decrease of absorbance (ΔA) was in good linear agreement with AA concentration in the range of 1.0-105 μM, with a low detection limit of 0.14 μM. The feasibility of this method was also investigated in commercial beverages with the 94.3-110.0% recovery.