Synthesis,Characterization And Application Of Nitrogen And Sulfur Doped Carbon Dots

Carbon dots(CDs)as a new family of nanomaterials have received wide attention in many fields such as bioimaging,biosensing and catalysis due to their simple synthesis and unique properties,such as good water solubility,easy functionalization,low toxicity,photoluminescence and excellent biocompatibility.However,there remain some challenges for CDs to be applied as fluorescent sensors.Doping CDs with heteroatoms,especially with N and S,is recently considered as an effective approach to change the band gap of the CDs,avoid self-quenching and tune their optical and electrical properties,and thus the quantum yield(QY)and sensitivity of the CDs are expected to be improved.In this thesis,the S,N-CDs were synthesized,characterized and used to detect lipoic acid,hemoglobin and hydrogen peroxide.The main research contents are as following:1.Synthesis and characterization of S,N-CDsA series of S,N-CDs were synthesized by hydrothermal method using citric acid,L-cysteine,thiourea,L-cystine,methionine and vegetables as raw materials.The structure and morphology of the as-prepared S,N-CDs were characterized by SEM,FT-IR and elemental analysis.Moreover,the luminescence performance of the S,N-CDs was explored by fluorescence spectrum.We found that the quantum yields of S,N-CDs gradually increased with the increase of S content.The quantum yield of the S,N-CDs with citric acid and L-cysteine as precursor was the highest.The results showed that all the obtained S,N-CDs had good monodispersion and water solubility,with a surface rich in functional groups such as-COOH,-NH₂,C-S and-SH.In addition,the S,N-CDs exhibited good photoluminescence stability,p H stability,high resistance to photobleaching and salt.2.Detection of lipoic acid(LA)using S,N-CDs as fluorescent probeWe found that the fluorescence of the S,N-CD₁with the quantum yield up to 55.72%was quenched after the addition of LA.The quenching mechanism between the S,N-CD₁and LA was considered to be attributed to the inner filter effect,which was discussed by fluorescence spectroscopy and UV-vis absorption spectroscopy.Under the optimal conditions,a linear relationship between the relative fluorescence intensity(F₀-F)/F₀and the LA concentration was obtained in the concentration range from 0.01 to 1.0 mg/mL with a detection limit of 4.1?g/mL.The method was simple,low cost and had a wide linear range,which shows great potential to be applied for the determination of LA in biological samples.3.Detection of hemoglobin(Hb)and hydrogen peroxide(H₂O₂)based on the“off–on”fluorescent probe of S,N-CD₁The S,N-CD₁showed stable blue fluorescence and good dispersibility in aqueous solution.It was found that the fluorescence of the S,N-CD₁could be quenched by Hb via?-?interaction.The UV-vis absorption spectra and fluorescence spectra confirmed the dynamic quenching mechanism of S,N-CD₁-Hb system.Upon the addition of H₂O₂to the system,the fluorescence of the quenched S,N-CD₁was restored.Therefore,the S,N-CD₁could be used as an efficient“off-on”fluorescent probe for the rapid detection of Hb and H₂O₂.A linear relationship between the relative fluorescence intensity(F₀-F)/F₀and the Hb concentration was obtained in the concentration range of 1 to 100?g/mL with a detection limit of 0.22?g/mL.By analyzing the relative fluorescence intensity(F-F₀)/F₀with the H₂O₂concentrations,we found a good linear relationship in the concentration range of 0.05 to 50mM.