Preparation Of Novel Fluorescent Nitrogen And Terbium-doped Carbon Dots And Their Analytical Application

Carbon dots(CDs)have attracted significant attention because of their unique luminescence,stable chemical properties,good water-solubility,low toxicity,outstanding biocompatibility,tunable surface functionalities and inexpensive.The application fields of CDs are also becoming more and more extensive,and have been successfully applied in biochemical analysis,biomedicine and catalytic photoelectroluminescent devices and so on.However,there are still some limitations or shortcomings in the synthesis and application.This paper has carried out the following work focuses on the synthesis and analysis application of CDs.Firstly,the N-CDs were synthesized via a simple hydrothermal synthesis method by using glucose,ethanol,ethylenediamine as the precursors.The Tb-CDs were prepared by doping with terbium ion in the basis of N-CDs.Then the size,component and spectral properties of the carbon dots were characterized by transmission electron microscope(TEM),infrared spectra(IR),fluorescence spectra(FL)and UV-vis absorption spectra(UV).The results showed that N-CDs are 20-30 nm in diameter and have a poor dispersion.However,the particle size of Tb-CDs became small and even,showing a good dispersion.Both of two carbon dots are rich in the structure of hydroxy,carboxyl and amide bonds on their surface,also nitrogen elements are effectively modified to carbon dots in the form of N-H and C-N.Compare with N-CDs,the fluorescence intensity of Tb-CDs was greatly enhanced,the quantum yield also increased from 7.84% to 9.05%.We studied the influence of N-CDs on the weak chemiluminescence system Na2SO3-H+-KMn O4 using flow injection analysis device,and established a chemical luminescence analysis method for the detection of sulfite in food.There is a linear relationship between with the concentration of Na2SO3 in the range of 3.0×10-5 ~ 8.0×10-4 mol L-1,the linear equation was lg I=1.56 lg C + 8.41(R2=0.991,n=8)and the detection limit was 6.8×10-6 mol L-1.This method was successfully applied to the determination of sulfite in fans and bean curds samples with recoveries in the range of 85.6% ~ 116%.Then the sensitization mechanism of N-CDs was investigated.It was suggested that N-CDs on the one hand could promote the generation of the excited state SO2*,on the other hand react with potassium permanganate becoming another emitters N-CDs* in the system,played the roles of sensitizer and emitter in the chemiluminescence reaction.The interaction between Tb-CDs and DNA has been studied,which revealed that the fluorescence intensity of the Tb-CDs could be quenched by DNA,then we established a fluorescence quenching method for the determination of DNA.There was a good linear relationship between lg(F0/F)and lg C in the range of 8×10-8 ~ 5×10-5 g m L-1.The linear equation was lg(F0/F)= 0.10 lg C + 0.03(C: 10-7 g m L-1,R2 =0.990,n =7),and the detection limit was 5.3×10-8 g m L-1.The method was applied in synthetic samples with recoveries in the range of 90.2% ~ 108.3%.The binding constants and thermodynamic constants were calculated by Stern–Volmer equation and thermodynamic equation,and the binding interaction between Tb-CDs and DNA was further investigated by UV-vis absorption spectra.The results suggested that the probable quenching mechanism was a static quenching procedure,hydrophobic forces were involved in the binding process.