A novel method for glucose detection using dual-modal carbon dots for colorimetric and ratiometric fluorescence analysis

Iron-based nitrogen co-doped carbon dots (Fe, N-CDs) were synthesized from taro leaf biomass via a hydrothermal process using ammonium ferric sulfate dodecahydrate and urea. The synthesized Fe, N-CDs exhibited peroxidase-like activity and strong fluorescence at 450 nm. A dual-mode colorimetric/ratiometric fluorescence assay for hydrogen peroxide (H₂O₂) detection was developed using Fe, N-CDs and o-phenylenediamine (OPD) as probes. In the presence of H₂O₂, OPD was oxidized to 2,3-diaminophenazine (DAP), which is yellow and absorbs at 420 nm. Under 360 nm excitation, DAP emits fluorescence at 550 nm and quenches the fluorescence of Fe, N-CDs at 450 nm due to the internal fluorescence filtering effect. This enables the quantitative analysis of H₂O₂ using the absorbance at 420 nm (A₄₂₀) and the fluorescence intensity ratio of DAP to Fe, N-CDs (I₅₅₀/I₄₅₀). Since glucose oxidase can convert glucose to H₂O₂, the assay was extended to glucose determination. At pH 5.4, 40 ℃, with 1.75 mmol/L OPD and a 25-minute reaction time, the method showed a linear relationship between the A₄₂₀ and I₅₅₀/I₄₅₀ values and glucose concentration in the range of 1.0~100 μmol/L, with detection limits of 0.8 μmol/L (colorimetry) and 0.6 μmol/L (ratiometry). The method was validated for glucose detection in human serum.