One-step synthesis of aldehyde-functionalized dual-emissive carbon dots for ratiometric fluorescence detection of bisulfite in food samples

[Display omitted] •Aldehyde functional dual-emissive CDs are readily obtained by one-step synthesis.•This fluorescent probe is developed for ratiometric detection of HSO3−.•The dual-emissive CDs are applied for the detection of HSO3− in food samples.•A smartphone-assisted sensing platform is used to detect HSO3− on-site. Bisulfite (HSO3−) is used as a food additive for its antibacterial and antioxidant properties. However, excessive intake of HSO3− is harmful to humans. Here, for the first time, aldehyde-functionalized dual-emissive carbon dots (D-CDs) are synthesized in one-step for direct ratiometric sensing of HSO3−. Due to the nucleophilic addition reaction between HSO3− and aldehyde of D-CDs, the fluorescence transforms from green to deep-blue. The linear range of the probe is 0.1–30 μmol/L with a detection limit of 42 nmol/L. Moreover, D-CDs show good selectivity and a fast reaction time (