Synthesis Of Novel Doped Carbon Quantum Dots And Application In Vitamin Detection

Carbon quantum dots（CDs）are widely applicated in chemical and biological sensor analysis due to advantages of unique and adjustable photoluminescence properties,easy synthesis,excellent light stability and biocompatibility.Doping of carbon quantum dots could improve the fluorescence characteristics and may give them new physical and chemical properties.Based on carbon quantum dots as signal probes with different properties,new methods for the detection of vitamin C（Vc）and vitamin B₁₂(VB₁₂)in medicines were established.In the chapter 1,the concept,synthesis route,the main detection mechanisms used to construct fluorescent sensors and the application in chemical sensing,bioimaging and drug delivery of carbon quantum dots are introduced.In addition,the main research contents of the article are expounded.In the chapter 2,iron-doped carbon quantum dots（Fe-CD）were green synthesized through one-step hydrothermal method using environmentally friendly materials-milk powder as precursor and Fe Cl₃as a dopant.It was found Fe-CD had photoluminescent properties and strong mimetic oxidase activity.Fe-CD can catalyze the oxidation of3,3’,5,5’-tetramethylbenzidine（TMB）to form the blue product ox TMB.The existence of Vc can reduce ox TMB and make the solution color lighter to realize the colorimetric determination of Vc.At the same time,we also found that the absorption peak of the ox TMB at 370 nm overlaps with the excitation spectrum of Fe-CD.ox TMB can quench the fluorescence of Fe-CD based on the IFE.The presence of Vc can reduce the ox TMB and recovery the fluorescence of Fe-CD.The change of fluorescence value（?F）is positively correlated with the concentration of Vc.Based on that,a new method of colorimetric/fluorometric dual-mode detection of Vc in pharmaceuticals is established.The linear range of the colorimetric method is 25.0～500μmol/L with the detection limit of 8.59μmol/L.The linear range of fluorescence method is 20.0～500μmol/L,the detection limit is 5.13μmol/L.The dual-signal detection method can eliminate false positives of single signal and improve the accuracy of detection results with great application prospect in the detection of Vc in drugs.In the chapter 3,proper precursors was selected to extend the emission of CDs to long wavelengths.Nitrogen and sulfur co-doped carbon dots（N,S-CDs）with orange fluorescence emission was synthesized through one-step hydrothermal method using o-phenylenediamine and thiourea as original materials.The N,S-CDs performed the largest emission peak at 565 nm under the maximum excitation of 420 nm.The absorption peak of vitamin B₁₂ at 550 nm overlaps with the emission peak of N,S-CDs in a large range,and based on the IFE between N,S-CDs and VB₁₂,a label-free,sensitive,and highly selective detection method of VB₁₂ in drug was established.Under the optimal conditions,the concentration of VB₁₂ performed a good linear relationship with the fluorescence quenching degree?F/F₀ of the reaction system at 565 nm in the range of 0.25-20μmol/L,the correlation coefficient r=0.9988,and the detection limit was 77.5 nmol/L.