Preparation And Analytical Application Of Fluorescent Carbon Dots Using Phenazine Dyes As Precursors

As the new type of luminescent nanomaterials,carbon dots are widely used in the fields of analysis,drug delivery,optical diagnosis,and anti-counterfeiting due to their excellent optical properties,good biocompatibility,low toxicity,etc.At present,most of CDs are limited in the short-wavelength emission and low quantum yield,thus impeding their subsequent biological applications.In addition,the current CDs-mediated analysis methods tend to single-mode and single-wavelength detection mode,which are susceptible to environmental factors.As an effective strategy to control the fluorescence properties,heteroatom doping paves the new way for improving the performance of CDs and expanding their multi-functional applications.In this work,a series of heteroatom-doped fluorescent carbon dots with long wavelength emission were designed using phenazine dyes as precursors,thereby constructing multifunctional and multi-mode fluorescence sensing platforms for detection of p H,ions and small molecules.Furthermore,the applications of these carbon dots in the field of bioimaging and solid-state luminescence devices were further explored.Chapter 1:The structure classification,optical properties,preparation methods and luminescent mechanism of carbon dots were briefly described.The research progress in the regulation of luminescent property and relevant applications were also reviewed.Chapter 2:Nitrogen-doped orange emission carbon dots（O-CDs）with excitation-independent wavelength properties were synthesized by solvothermal treatment using saffron T as precursor.Based on the largeπconjugated structure of raw materials,the sensitive detection method for vitamin B₁₂(VB₁₂)and peroxynitrite（ONOO^-）was established,and the corresponding fluorescence quenching mechanisms in the detection process were explored.VB₁₂ could effectively quench the fluorescence of O-CDs on the basis of internal filtration effect.The fluorescence assay via O-CDs could sensitive assess VB₁₂ in the linear range of 1–65μM and 70–140μM with a detection limit of 0.62μM.In addition,ONOO^-could reduce the fluorescence intensity of O-CDs based on static quenching（SQ）.The linear ranges were 0.3–9μM and 9–48μM,and the detection limit was 0.06μM.Based on the excellent biocompatibility and low cytotoxicity,O-CDs were also successfully applied in cellular imaging of VB₁₂ and endogenous/exogenous ONOO^-.In addition,the O-CDs were further used in the field of solid-state luminescent materials by engineering O-CDs/PVA based fluorescent flexible film,which proved that O-CDs had broad application prospects in the fields of fluorescence sensing,cell imaging and solid-state luminescence materials.Chapter 3:Orange emission carbon dots（O-CDs）with quantum yield of 54.4%were synthesized using nile blue sulfate and citric acid as precursors.Morin and Cl O^-could interact with the surface structure of O-CDs respectively,thus quenching the fluorescence of O-CDs.The O-CDs based fluorescent method could detect morin in the linear range of5–125μM with the detection limit of 0.84μM.Meanwhile,it also demonstrated satisfactory responsiveness toward Cl O^-in the linear range of 2.5–90μM with the detection limit of 0.46μM.The obtained O-CDs had successfully realized the monitoring of morin and endogenous/exogenous Cl O^-in living cells and zebrafish owing to its superior biocompatibility,exceptional photostability and lower toxicity,which provided a new idea for the early diagnosis of related diseases.Chapter 4:Nitrogen and sulfur co-doped orange emission carbon dots with excitation-dependent wavelength（N,S-CDs）were synthesized by one-step hydrothermal method using neutral red and DL-methionine as precursors.Due to the functional group on the surface of N,S-CDs,a dual-functional fluorescence sensing platform for profiling p H and arginine（Arg）was constructed.Taking advantage of the protonation and deprotonation of nitrogen-containing functional groups on the surface of N,S-CDs,the sensitive detection of p H in the range of 4.8-8.2 was realized.Based on the static quenching effect,Arg could quench the fluorescence of N,S-CDs.The linear range of 2.5-62.5μM and detection limit of 0.68μM,thus ensuring the assessment of Arg in real samples along with good recovery and low relative standard deviation.In addition,N,S-CDs were further used for the detection of p H and Arg in living cells and zebrafish and preparation of fluorescent composite films,which had potential application value in the field of fluorescence sensing and clinical diagnosis.Chapter 5: Label-free ratiometric fluorescent carbon dots（O-CDs）were synthesized by one-step hydrothermal method using neutral red and polyimide as precursors.The special structure on the surface of O-CDs could combine with Ser,resulting in a new emission peak at 533 nm for O-CDs,while the emission peak at 593 nm unchanged.In addition,with introduction of GSH,GSH could be competitively combined with Ser to decompose OCDs@Ser complex,then the fluorescence of O-CDs restored.The ratiometric detection of Ser and GSH could be achieved by calculating the ratio of the emission peak of O-CDs at 533 nm and 593 nm and the reversible fluorescence change of "orange-green".Based on this phenomenon,the smartphone detection strategy was established to realize the visual detection of Ser and GSH.The O-CDs also could be utilized for the detection of Ser and GSH in real samples,and revealed good recovery and low relative standard deviation.Moreover,O-CDs are further employed for label-free ratiometric monitoring of Ser and GSH in living cells and preparation of fluorescent composite materials,which demonstrated that O-CDs was a promising long-wavelength carbon-based nanomaterial for ratiometric detection,smartphone sensing and solid-state luminescent materials.