S,O-doped carbon nitride as a fluorescence probe for the label-free detection of folic acid and targeted cancer cell imaging

A novel nanoprobe based on S,O-doped carbon nitride quantum dots (S,O-CNQDs) was designed and synthesized. The as-prepared S,O-CNQDs exhibits good biocompatibility and strong fluorescence at excitation 360 nm. It is found that folic acid (FA) could efficiently quench the fluorescence of S,O-CNQDs. The obtained S,O-CNQDs is capable of acting as a sensitive and selective probe for FA detection in the range 5.0–83.3 μM with a detection limit of 90 nM. The as-prepared probe has been successfully utilized for the detection of FA in various real samples with satisfactory recoveries (98.8–107 %) and small relative standard deviation (<5%). The reaction mechanism between S,O-CNQDs and FA has been discussed. In addition, FA-S,O-CNQDs formed through a classical cross-linking reaction between FA and S,O-CNQDs easily accesses and penetrates into HepG2 cells with high folate receptors expression. FA-S,O-CNQDs with low cytotoxicity and good biocompatibility shows great potential in FA detection and targeted imaging of cancer cells.