Multifunctional ratiometric fluorescent sensing platform constructed by grafting various response groups on carbon dots with bromine active site for biosensing and bioimaging

Multifunctional sensing platform with the advantages of simplicity, convenience and efficiency is critical to the improvement of application in biosensing and bioimaging. However, the lack of easily modified scaffold materials seriously hinders its various responsive sensing development. To solve this issue, a novel kind of carbon dots (namely rCDs) with easily modified bromine substitution site was developed by one-step solvothermal treatment of citric acid, ethylenediamine and 4-bromo-1,8-naphthalic anhydride. Benefiting from the maintained structure of naphthalimide structure with bromine substitution site to contribute responsive yellow-green fluorescence emission and the stable blue fluorescence emission from citric acid and ethylenediamine, dual emissive ratiometric sensors based on rCDs could be conveniently fabricated by avoiding the combination of two components with distinct emission wavelength together. As proof, three ratiometric fluorescent probes for sensing formaldehyde (rCDs-FA), HSO3- (rCDs-HSO3-) and pH (rCDs-pH) featuring high stability, selectivity and biocompatibility were simply prepared. Moreover, the as-obtained probes were successfully applied to monitor dynamic variations of formaldehyde, HSO3- and pH changes in living cells. Taken together, the established multifunctional ratiometric fluorescent sensing platform could be simply and effectively regulated through changing the grafted response groups. This work would provide a universal method to design more biosensing or bioimaging platforms by adjusting response groups in the future.