Surface modification of carbon quantum dots by fluorescein derivative for dual-emission ratiometric fluorescent hypochlorite biosensing and in vivo bioimaging

Surface modification of carbon quantum dots by fluorescein (FH-GA-CQDs) were synthesized for dual-emission ratiometric fluorescent ClO− biosensing and in vivo bioimaging. In the presence of ClO−, FH-GA-CQDs solution shows gradually decrease in the emission intensity at 413 nm and rapidly increase in the emission at 508 nm, corresponding to the blue-to-green emission color change. The detection mechanism is that the ClO− induces the ring-opening of FH units to form an oxadiazole structure, resulting in energy transferring from CQDs moiety to FH units. The energy transfer efficiency and energy transfer rate were estimated as 0.34 and 4.00 × 10−7 s−1, respectively. The results reveal that the FH-GA-CQDs have high sensitivity and selectivity for ClO− in the linear range extending from 0 to 70 μM with a detection limit as low as 93 nM. Meanwhile, the potency of the FH-GA-CQDs detecting ClO− in real water examples were validated by recoveries from 94% to 106% and semi-quantification determination of ClO− on fluorescent test strips. Most importantly, FH-GA-CQDs display low cytotoxicity and were successfully applied for sensing of ClO− in living cells and imaging of ClO− in nude mice.