Mustard seeds derived fluorescent carbon quantum dots and their peroxidase-like activity for colorimetric detection of H2O2 and ascorbic acid in a real sample

Highlights: • Green precursor and ecofriendly route were applied for the synthesis of fluorescent carbon quantum dots. • The synthesized M-CQDs showed peroxidase like activity to oxidize the TMB in presence of H₂O₂ via ping- pong mechanism. • The H₂O₂ dependent oxidation of TMB by M-CQDs act as sensor for detection of H₂O₂ with lower limit up to 0.015 mM. • Interestingly, ox-TMB further reduced to native form by ascorbic acid with good selectivity and sensitivity. • The ox-TMB based sensing showed excellent practical feasibility for the detection of AA in edible fruits viz. real sample. -- Abstract: Herein, we were synthesized fluorescent carbon quantum dots via facile one-step hydrothermal treatment of mustard seeds (M-CQDs). It showed excellent optical property with fluorescent quantum yield 4.6%. The as-prepared M-CQDs exhibited peroxidase-like mimetic activity and catalyzed the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to produce a blue color reaction mixture with the prominent peak at 652 nm. Furthermore, the peroxidase-like catalytic performance of M-CQDs followed the steady-state kinetics behavior and exhibited similar catalytic activity as that of natural enzyme Horseradish peroxidase (HRP). In addition to this, the double reciprocal plot showed a parallel line which suggested the occurrence of Ping-Pong type of mechanism. The H₂O₂ dependent oxidation of TMB was helpful for the colorimetric detection of H₂O₂ in the linear range of 0.02–0.20 mM with the limit of detection (LOD) of 0.015 mM. Interestingly, the oxidized TMB (ox-TMB) was further reduced to native TMB by the reducing agent ascorbic acid. Hence M-CQDs showed its potential towards the selective and sensitive detection of ascorbic acid in the linear range of 10–70 μM having a correlation coefficient of 0.998 with LOD of 3.26 μM. The practical feasibility of the proposed detection method of AA was also investigated in common fresh fruits.