Green and facile synthesis of iron-doped biomass carbon dots as a dual-signal colorimetric and fluorometric probe for the detection of ascorbic acid

Iron-doped carbon dots (Fe-CDs) were greenly synthesized via a one-step hydrothermal method using the eco-friendly materials milk powder and FeCl3. It was found that the synthesized biomass Fe-CDs have photoluminescence properties and strong mimetic oxidase activity, which enables catalysis of the oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB) to produce a blue product, oxidized TMB (oxTMB). The presence of ascorbic acid (AA) could reduce the oxTMB and make the solution color lighter to realize the colorimetric determination of AA. In addition, the absorption peak of the oxTMB generated at 370 nm overlaps with the excitation spectrum of Fe-CDs, and oxTMB quenched the fluorescence of Fe-CDs based on the internal filtration effect (IFE). The presence of AA will reduce oxTMB and restore the fluorescence of Fe-CDs, and the change of fluorescence intensity is positively correlated with the concentration of AA. Accordingly, a novel method for colorimetric/fluorometric dual-signal detection of AA was developed. The linear range of the colorimetric assay was 25.0-500.0 mu M, and the detection limit was 8.59 mu M. The linear range of the fluorometric assay was 20.0-500.0 mu M with an LOD of 5.13 mu M. The method took advantage of different signals to achieve complementarity and eliminate false positives of single signals and improve the accuracy with great application prospects in the detection of AA.