The Synthesis,Characterization And Applications Of Fluorescent Doped Carbon Dots

Objective:As a new kind of carbon nanoparticles,fluorescent carbon dots?CDs?have been widely applied in various types of fields including fluorescent probe,photocatalyst,bio-imaging and fluorescent chemosensor,due to their outstanding optical properties,excellent biocompatibility,superior aqueous solubility and lower toxicity.Although fluorescent CDs have many advantages,the quantum yield?QY?of CDs by previous chemical syntheses is lower,which has greatly limits their practical applications in fields such as chemosensor,drug delivery system,bio-imaging,etc.Scientists have used different methods to improve the QY and found that doping heteroatoms with CDs is the most useful method to improve the QY.Therefore,synthesizing the doped CDs with high quantum yield and exploiting their applications in the field of pharmaceutical analysis has great application values.Methods:In this paper,boron and nitrogen co-doped carbon dots?BNCDs?,nitrogen and sulfur co-doped carbon dots?NSCDs?were both successfully synthesized by using the microwave heating method.The BNCDs and NSCDs were characterized by multiple analytical techniques,such as Transmission electron microscope?TEM?,X-ray diffraction?XRD?,Fourier transform infrared spectrum?FT-IR?,X-ray photoelectron spectra?XPS?and so on.The optical properties of BNCDs and NSCDs were investigated by Ultraviolet-visible absorption spectrum?UV-Vis?and fluorescence emission spectra.The BNCDs could be used as a sensitive fluorescence probe for the detection of Hg²⁺ in real water samples and curcumin in practical samples,respectively.The fluorescence of NSCDs could be obviously quenched by Hg²⁺.Subsequently,with the addition of glutathione?GSH?,the fluorescence of the NSCDs-Hg²⁺ system was gradually restored.On account of this phenomenon,we constructed a convenient "Turn off/on" fluorescence probe for the detection of GSH.Results:The morphology,elemental and functional groups composition of the BNCDs and NSCDs were characterized respectively.A sensitive fluorescence probe based on the BNCDs was used to detect Hg²⁺ and curcumin.The detection limit of Hg²⁺ ion was 2.3 nM with the linear range of 0.04-22.00 ?M.The detection limit and linear range of curcumin were 65 nM and 0.2-12.5 ?M,respectively.This method has been successfully applied for the detection of Hg²⁺ in tap and lake water samples with good reoveries of 99.8-101.8%.The reoveries of detecting the curcumin in human urine and serum samples were in the range from 96.5%to 105.5%.The NSCDs have been synthesized and used as a convenient "Turn off/on" fluorescence probe for the detection of GSH.After the addition of Hg²⁺,the fluorescence of the NSCDs quenched remarkably.The fluorescence of the NSCDs-Hg²⁺ system was in the "off" process.The "on" process was realized by the introduction of GSH in the NSCDs-Hg²⁺ system,which restored the fluorescence of NSCDs-Hg²⁺ system.This "on" process was applied to detect GSH,the detection limit was 52 nM and the linear range was 0.5-34.0 ?M.Conclusion:Because of the phenomenon of Hg²⁺ and curcumin could quenched the fluorescence of BNCDs,the methods for the detection of Hg²⁺ and curcumin were presented.The main quenching mechanisms between BNCDs and Hg²⁺ was static quenching.The main quenching mechanisms between BNCDs and curcumin was inner filter effect?TFE?and dynamic quenching.A convenient "Turn off/on" fluorescence probe based on the NSCDs has been used for detecting the GSH in human urine and serum samples with the satisfactory results.The mechanisms of the fluorescence quenching and restoring of NSCDs have been discussed.Dynamic quenching was the main quenching mechanism between NSCDs and Hg²⁺.The fluorescence of the NSCDs-Hg²⁺ system was recovered gradually with the addition of GSH owing to its stronger affinity with Hg²⁺.