Construction Of Fluorescent Probes Based On Long-wavelength(Red And Near Infrared) Emissive Carbon Dots And Their Sensing Application

Carbon dots?CDs?,as a new type of fluorescent nanomaterials,have attracted many researchers interest over the past ten years.In comparison with semiconductor quantum dots and organic fluorescent dyes,CDs possess many significant advantages,such as easy preparation,no/low toxicity,excellent physicochemical stability and unique photophysical properties.As a consequence,CDs have gradually been widely applied in the fields of sensing,catalysis,bioimaging and optoelectronic devices.In view of above,on one hand,we have designed disulfide bond-based self-crosslinked red carbon dots?SCCDs?as fluorimetric“turn-on”nanoprobe for intracellular GSH detection and imaging.On the other hand,the prepared near-infrared carbon dots?NIR-CDs?were used as a highly efficient and sensitive fluorescent probe,for the detection of metal cations i.e.Cu²⁺.The specific work contents are as following:?1?The thiol group was modified on the surface of the CDs through amidation reaction between 3-mercaptopropionic acid and red carbon dots?RCDs?,and then the self-crosslinked red carbon dots?SCCDs?can be obtained under the oxidation of H₂O₂.It was found that the fluorescence emission intensity of the designed SCCDs nanoprobe was significantly reduced,owing to the effect of aggregation induced quenching.Based on the principle of GSH selective reduction of disulfide bond,the SCCDs were disassembled into free CDs in the presence of GSH.As a consequence,fluorescence of the SCCDs was recovered in a GSH concentration-dependent manner,which laid the foundation for the quantitative analysis of GSH.Moreover,the experimental results showed that the response of the nanoprobe to GSH exhibited prominent selectivity and sensitivity,which have a linear range from 0 to 0.15 m M,with a limit of detection?LOD?of 5.7?M.In addition,at the cellular level,the nanoprobe was indicated to be extremely low cytotoxicity,and in the end can be successfully applied for the detection of intracellular GSH level.?2?Using glutathione and polyethyleneimine?PEI?as reaction raw materials,carbon dots with long-wavelength near-infrared emissive characteristics?NIR-CDs?can be prepared in formamide as solvent through a simple solvothermal reaction.The morphology,surface structure and optical properties of NIR-CDs were analyzed.The results have revealed that the as-synthesized NIR-CDs exhibited excellent optical stability and good solubility.Subsequently,a highly efficient and sensitive fluorescent experimental results have manifested that when the concentration of Cu²⁺was in the range of 0.2-0.5?M,which has a good linear relationship with the quenching degree of NIR-CDs,and the detection limit is 7.4 n M.