Preparation Of Conjugated Enhanced Red Light Carbon Dots And Its Application In Fluorescence Detection

The fluorescence detection method is widely used in the quantitative analysis and detection for its advantages of simplicity,quick response time and high sensitivity.As a new class of fluorescent carbon nanomaterials,carbon dots?CDs?have some unique advantages,such as good optical properties,excellent biocompatibility,and multicolor photoluminescent,which make them become a promising tool in the field of fluorescence detection.Most reported CDs showed blue or green light emission,which is not suitable for biological imaging/biomedicine because of high background signal,poor cell/tissue penetration,and damage to cell/tissue which restricts their applications.Therefore,it is an urgency to obtain long-wavelength and red emission of CDs for further applications in the field of biomedical and fluorescence detection.In this work,based on the photoluminescence mechanism of CDs,two types of red emission carbon dots are synthesized by enhancing the conjugated structure of carbon dots from suitable carbon source simple hydrothermal/solvothermal method.The prepared CDs show multiple applications in the detection of inorganic ions,trace water,bioimaging and solid-state lighting.The research is conducted as follows:?1?Preparation of porphin-based red emission carbon dots and their applications in phosphate(PO₄^3-)detection.Porphin-based carbon dots?PCDs?were prepared through a one-step hydrothermal method by using meso-tetra?4-carboxyphenyl?porphine?TCPP?,citric acid and ethanediamine as precursors.PCDs gave rise to the optimal photoluminescence at?_ex/?_em=375/645 nm,exhibit an excitation-independent property,excellent water solubility,and good biocompatibility,which provided red emission and avoid the autofluorescence as an efficient fluorescence imaging probe.On the other hand,when Eu3+is added into PCDs,the carboxylate groups located on the surface of PCDs exhibit high affinity to Eu³⁺,resulting in the fluorescence of PCDs turning off via static quenching.In the presence of phosphate,owing to the strong coordination with Eu³⁺,the fluorescence of PCDs turns on.Based on this performance,a novel“turn off-on”phosphate sensing system is developed.The detection limit of this sensing system can attain 3.59×10^-3?mol L^-1.This system has been utilized for the detection of phosphate in real samples successfully,which further demonstrates potential applications in biological diagnostic and environmental analysis.?2?Binaphthyl-based red emission carbon dots and their applications in trace water detection in organic solvents and fluoride ion detection.In this study,1,1'-binaphthyl-2,2'-diamine?BNDM?and citric acid were used as precursors and toluene was used as a solvent by a simple one-pot solvothermal method to synthesize binaphthyl-based red emission carbon dots?BNCDs?.The synthesized BNCDs have uniform size distribution,photobleaching resistance,and excitation wavelength-independent fluorescence emission performance with the optimal fluorescence at?_ex/?_em=540/603 nm.The composite films of BNCDs in polyvinyl alcohol?PVA?matrix were exhibited obvious red emission under ultraviolet irradiation,indicating their potential in solid-state luminescence.Also,through the investigation of the hydrophobicity of BNCDs in different kinds of organic solvents,we found that BNCDs can be used as a fluorescence sensor for highly sensitive quantitative detection of trace water in organic solvents.The study also demonstrated that the fluorescence of BNCDs can be effectively quenched by Fe³⁺,while F^-can be desorbed from the carbon dots through the strong coordination of F^-with Fe³⁺to restore the fluorescence of BNCDs.Based on this phenomenon,potential applications of BNCDs for F^-detection can be realized.