A colorimetric and fluorescence dual-signal determination for iron (II) and H₂O₂ in food based on sulfur quantum dots

A colorimetric and fluorescence dual-signal method based on sulfur quantum dots (SQDs) was established for determination of iron (II) (Fe2+) and H2O2 in foods. Due to the complexation of Fe2+ with SQD, Fe2+ can cause fluorescence quenching of SQDs, and the color of the mixed solution changed from light yellow to deep green. By use of Fenton reaction, H2O2 can restore the quenched fluorescence of SQDs, and the color of the mixture changed from green to colorless. The concentration of Fe2+ and H2O2 has a good linear relationship with the fluorescence intensity and absorbance in the range of 2.5-55 mu M and 1.25-500 mu M, and the detection limits were 1.41 mu M and 0.54 mu M, respectively. For determination of H2O2, the linear ranges were 1.17-1.97 mM and 0.867-1.50 mM, and the detection limits were 0.03 mu M and 0.06 mu M, respectively.