Smartphone colorimetric determination of hydrogen peroxide in real samples based on B, N, and S co-doped carbon dots...

In this paper, we report the use of a smartphone and B, N, and S co-doped carbon dots (BNS-CDs) as a promising peroxidase mimic to quantify hydrogen peroxide (H₂O₂). The synthesized BNS-CDs exhibited excellent peroxidase-like activity to catalyze the reaction of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂ to generate a blue oxide product (ox-TMB) with maximum absorption at 652 nm. Steady-state kinetic analysis demonstrated that the BNS-CDs showed much higher affinity than natural horseradish peroxidase (HRP) for H₂O₂ due to their small size and larger specific surface area. A smartphone colorimetric readout device was employed to record the RGB (red green blue) value of the ox-TMB solution via the Android application Color Grab for quantitative detection. A good linear relationship (R² = 0.9970) between the H₂O₂ concentration and |R-R_blank| value was obtained in the range of 3-30 μM with a limit of detection (LOD) of 0.8 μM. The current method was successfully applied to determine H₂O₂ in mouthwash and milk with recoveries of 92.70-108.30%. The developed assay is a promising portable detection platform for H₂O₂ with good sensitivity and selectivity, simple operation, fast response, and low cost. Graphical abstract.