Synthesis Of Carbon Dots And Its Application As A Fluorescent Probe For Detection Of ClO^- And HSO₃^-

Hypochlorite,as one of the reactive oxygen species（ROS）,is endogenously generated by the peroxidation of chloride ions catalyzed through the enzyme myeloperoxidase（MPO）.It plays a vital role in immune processes due to its powerful oxidation.In addition,bisulfite can be endogenously generated during the scavenging of ROS.Thus,its generation is closely connected to the physiological processes of redox balance and aging.On the other hand,abnormal levels of bisulfite and hypochlorite can lead to some diseases.Therefore,the development of a novel,fool proof and sensitive technique for detecting hypochlorite and sulfite is imminent.Currently,the developed flouresent probes to detect ClO^-and HSO₃^-are almost a based on organic fluorophores.Unfortunately,the organic fluorophores suffer from poor molecular stability and complex preparation,which limit their further application.Carbon dots（CDs）is a new member of the carbon nanomaterials family.Due to its good water solubility,biocompatibility,light stability and easy modification,it is very attractive in the development of biosensors.In this work,nitrogen-doped carbon dots（N-CDs）were synthesized by a simple one-step solvothermal method using glutathione（GSH）and urea as precursor,ethanol as solvent.The prepared N-CDs have good dispersion and uniform particle size distribution in the range of 10-16 nm.These CDs exhibit stable fluorescence under ultraviolet excitation.They dispaly both excitation-independence and excitation-dependent emission characteristics,due to carbon core states emission and surface defect emission states,respectively.The strongest emission was observed at 420 nm under 340 nm excitation with the QY of 8.6%.When the concentration of N-CDs reaches 800μg mL^-1 and the culture time is 24 h,no significant cytotoxicity is observed in the MTT test.It has been found that ClO^-can quench the fluorescence of N-CDs by destroying the surface passivation layer of N-CDs.Therefore,a"turn-off"mode fluorescent probe has been established on basis of N-CDs for detecting ClO^-.At the optimized experimental conditions,the probe exhibited high sensitivity and selectivity to ClO^-with the detection limit（LOD）of 3.4μM.In addition,with the introduction of HSO₃^-,the sulfo group content attached to the surface of N-CDs increased,which could effectively restore the quenched fluorescence of N-CDs.The above phenomenon demonstrated the feasibility of N-CDs/ClO^-as a"turn-on"mode fluorescent probe to detect HSO₃^-.This probe could specifically recognize HSO₃^-with high sensitivity（LOD=0.27μM）.In addition,due to their low toxicity and fast response,the prepared N-CDs were successfully applied to detect ClO^-and HSO₃^-in living cells.