Ratiometric fluorometric and colorimetric dual-signal sensing platform for rapid analyzing Cr(VI), Ag(I) and HCHO in food and environmental samples based on N-doped carbon nanodots and o-phenylenediamine

Nitrogen-doped carbon nanodots (N-CNDs) were synthesized simply and efficiently using glutathione. The fluorescence emission of N-CNDs at 430 nm was effectively quenched by the fluorophore 2,3-diaminophenazine (DAP), produced through the oxidation of o-phenylenediamine (OPD) under the catalysis of Cr(VI)/Ag(I). This quenching was attributed to the fluorescence resonance energy transfer effect, while a new fluorescence emission at 560 nm was observed. Furthermore, the redox and chromogenic reaction of Cr(VI) and OPD at pH 5.4 could be effectively inhibited by formaldehyde (HCHO), resulting in the activation of N-CNDs fluorescence and the quenching of DAP fluorescence. Consequently, dual-signal sensing platforms for the rapid analysis of Cr(VI) and Ag(I) using N-CNDs/OPD and HCHO using N-CNDs/OPD/Cr(VI) were successfully constructed. By incorporating a masking reagent such as H2O2 for Cr(VI) and Cl- for Ag(I), the established sensing platform exhibited excellent selectivity and practical applicability for detecting Cr(VI), Ag(I), and HCHO in food and environmental samples.