Preparation Of Novel Fluorescent Carbon Dots And Their Applications For Ions,Small Molecules Determination And Cell Imaging

Carbon dots?CDs?are a new class of fluorescent nanomaterials that have been developed over the past decade.Owing to the small particle size,good stability against photobleaching,high fluorescence stability,tunable fluorescence emission,easy surface functionalization,low toxicity and excellent biocompatibility,CDs have a broad application prospect in many fields including catalyst,cell imaging,drug delivery,fluorescence detection and photoelectronic device.However,there are still some problems needing to be solved,such as unclear luminescence mechanism and narrow spectral coverage.The mainly fluorescence color of many CDs is in the region of blue,green and yellow.In order to reduce the autofluorescence interference of biological samples,it is of great significance to develop new methods for synthesizing red fluorescent CDs and explore their applications in life analytical chemistry.Based on the previous study,new methods for the simple and rapid synthesis of novel fluorescent CDs have been developed in this dissertation.Additionally,the CDs can be served as fluorescent probes and their applications in the field of analytical chemistry have been studied.In this dissertation,the following innovative researches have been carried out.?1?Nitrogen-doped CDs?N-CDs?with fluorescence quantum yield up to 36%were prepared by a solid-phase synthesis strategy.A new fluorescent method has been established based on the N-CDs probe for the rapid and sensitive detection of trace Hg²⁺in food and cosmetics samples.In addition,the corresponding determination mechanism was also studied.?2?A“switch-on”CDs-MnO₂ probe based on CDs and MnO₂ nanosheets was fabricated and a new fluorescent method has been established for the detection of ascorbic acid?AA?in fresh fruits,vegetables and commercial fruit juice samples.In addition,the determination mechanism of the CDs-MnO₂ probe toward AA was also investigated.?3?The red/green dual emissive CDs?RGDE CDs?with two emission peaks at525 nm and 603 nm were synthesized by a one-pot method,which can be directly utilized for peroxynitrite?ONOO^-?determination.A new ratiometric fluorescent method has been established for the determination of trace ONOO^-in cells based on the RGDE CDs fluorescent probe.?4?The red/yellow dual emissive CDs?RYDE CDs?and red/orange dual emissive CDs?RODE CDs?were simultaneously synthesized by a one-pot method.A new ratiometric fluorescent method has been established for the determination of trace nitrite in bacon,sausage,pickle and milk samples based on the RYDE CDs fluorescent probe.Additionally,the RYDE CDs was successfully applied for cell imaging.This dissertation consists of six chapters.Chapter 1:In this chapter,the raw materials,methods and effect of heteroatom doping for the synthesis of CDs were summarized.The strategies for fabricating fluorescent probes by CDs and the possible determination mechanisms were stated.Applications of the CDs in fluorescence detection,bioimaging,drug and gene delivery,catalysis,optoelectronic devices and anti-counterfeiting technology were reviewed.Chapter 2:According to the properties of Hg²⁺,citric acid and?NH₄?₃PO₄ were respectively used as carbon and nitrogen sources to synthesize nitrogen-doped CDs?N-CDs?with high fluorescence quantum yield of 36%and strong coordination ability with Hg²⁺by a solid-phase synthesis strategy.Based on the phenomenon of fluorescence quenching induced by the synergistic coordination between Hg²⁺and pyrrolic-like N and N-H on the surface of N-CDs,a new fluorescent method has been established for simple and rapid detection of Hg²⁺.The determination mechanism was studied.Under the optimal conditions,the linear range were 0.006-0.9?M and0.9-12.0?M with the limit of detection was 2.3 nM.The method was successfully applied for the detection of Hg²⁺in food and cosmetics samples with the recoveries of90%-106%.Owing to the low cytotoxicity and good biocompatibility,the N-CDs were successfully used for cell imaging.In addition,the feasibility of N-CDs served as fluorescent ink was also evaluated due to their good water solubility.Chapter 3:CDs and MnO₂ nanosheets were combined by inner filter effect?IFE?to fabricate the CDs-MnO₂ probe.Based on this,a new fluorescent method was established for the detection of ascorbic acid.The fluorescence quenching and recovery mechanisms were respectively studied.Under the optimal conditions,the linear range was 0.18-90?M with the limit of detection was 42 nM.This method was low-cost and environmentally friendly,and exhibited a wide linear range,high sensitivity,excellent selectivity and rapid response.Visual determination of ascorbic acid was also realized.Additionally,the method was successfully applied for the determination of ascorbic acid in fresh fruits,vegetables and commercial fruit juice samples with the recoveries of 95%-105%.Chapter 4:The red/green dual emissive CDs?RGDE CDs?with dual emissive peaks at 525 nm and 603 nm were synthesized by a one-pot method.Based on the fact that the RGDE CDs can be used as a fluorescent probe without any modification toward peroxynitrite?ONOO^-?,a new ratiometric fluorescent method for the detection of ONOO^-with low cost,rapid response,high sensitivity and good selectivity was established.Under the optimal conditions,the linear range was 0.03-60?M with the limit of detection was 11.6 nM.By calculating the HOMO and LUMO energy levels of RGDE CDs and ONOO^-,the mechanism of fluorescence quenching of RGDE CDs induced by ONOO^-has been deeply studied,and the conclusion was drawn that the mechanism may be caused by electron transfer.Additionally,this ratiometric fluorescent probe was successfully applied for the determination of trace ONOO^-in living cells.Chapter 5:The red/yellow dual emissive CDs?RYDE CDs?and red/orange dual emissive CDs?RODE CDs?were simultaneously synthesized by a one-pot strategy.Based on the fact that the RYDE CDs can be directly used as a fluorescent probe without any modification toward nitrite,a new ratiometric fluorescent method for the detection of trace nitrite in bacon,sausage,pickle and milk samples was established.The possible determination mechanism was investigated.Under the optimal conditions,the linear range was 0.1-100?M with the limit of detection was 31.61 nM.Owing to the influence of temperature on the fluorescence intensity of RYDE CDs,a new ratiometric fluorescent method for the detection of temperature was also established.Moreover,the RYDE CDs was successfully applied for cell imaging.Chapter 6:Conclusion.