Ratiometric fluorescent nanoprobes based on coumarin dye-functionalized carbon dots for bisulfite detection in living cells and food samples

As an important food additive, extensive intake of bisulfite (HSO3-) often leads to serious related diseases. However, the reliability and accuracy of HSO3- detection remains an outstanding challenge because the majority of previously reported sensors for HSO3- have been evaluated by the single-channel signal output. Herein, we constructed a ratiometric fluorescent nanoprobe, Coum-CDs, by covalently coupling the coumarin dye (Coum) onto the surface of yellow emissive carbon dots (Y-CDs) via amide bonds. The Coum-CDs themselves showed peculiar dual fluorescence emission at 480 and 565 nm under single-wavelength excitation. However, upon treatment with HSO3-, the pi-conjugation structure of Coum was destroyed due to the selectively nucleophilic reaction between the C-4 atom of Coum and HSO3-, which shut off the pathway of fluorescence resonance energy transfer from Coum to Y-CDs. As a result, the fluorescence emission of Coum-CDs at 565 nm decreased significantly, accompanied by a slight change in fluorescence intensity at 480 nm, allowing the ratiometric detection of HSO3-. In addition, the nanoprobe Coum-CDs displays a very low detection limit of 15 nM and excellent selectivity without interference from other relevant analytes, especially reactive sulfur-containing species. Importantly, preliminary experiments showed that the Coum-CDs have been successfully applied to ratiometric monitoring of exogenous and endogenous HSO3- in living cells, as well as the quantitative measurement of HSO3- in sugar and wine.