Preparation And Performance Research Of Magnetic Resonance/Fluorescence Bimodal Imaging Probe Based On Carbon Quantum Dots

In recent years,the incidence of cancer has increased annually,and it has become the most serious disease that threatens human life and health.Early diagnosis of cancer through molecular imaging techniques such as magnetic resonance imaging?MRI?,fluorescence imaging?FI?,and ultrasound imaging is crucial to improve the cure rate and improving patient prognosis.However,in clinical application,each tape of molecular imaging technology has its own limitationsin terms of selectivity,resolution,sensitivity,etc.Therefore,multimodal imaging,which combines two or more modalities,takes complementary strengths of various imaging techniques to obtain more comprehensive and accurate diagnostic information,has become one of the important directions of imaging development.Among them,the most critical element for the realization of multimodal imaging is the construction of multimodal imaging probes.Regarding this,this paper focuses on the preparation and performance of MRI/FI multimodal imaging probes based on carbon quantum dots.The main research work is as follows:?1?Using citric acid and urea as precursors,four new types of carbon quantum dots?CQDs-1,CQDs-2,CQDs-3 and CQDs-4?were synthesized in different eutectic solvents?U-DES and O-DES?by different preparation methods.The determination technologies including XRD,TEM,FTIR,Raman and XPS were used to characterize the chemical composition and morphology of four types of carbon quantum dots.The optical properties of the four types of carbon quantum dots were studied by UV-Vis absorption spetra and fluorescence spectroscopy,and the results showed that they exhibited blue,green,and red fluorescence emissions in aqueous solutions,respectively.Cytotoxicity analysis of the prepared CQDs-1 and CQDs-2 by MTT method confirmed that the CQDs had good biocompatibility and low cytotoxicity.The confocal laser scanning microscope?CLSM?images of CQDs-1 and CQDs-2 on mouse mononuclear macrophages?RAW264.7?were studied.CQDs-1 and CQDs-2showed blue,green and red color at the excitation wavelengths of 360,405 and 488nm,respectively.At the same time,its performance as a fluorescent imaging probe in RAW264.7 imaging at different uptake times was also investigated.?2?On the basis of work?1?,the coordination complexes of Gd?III?citrate?Gd?Cit?·2H₂O?was prepared and used as a precursor to prepare the T₁ type MRI/FI bimodal probe Gd-CQDs-4 in O-DES.The chemical composition and structure morphology of Gd-CQD-4 were characterized by XRD,TEM,FTIR and XPS.The optical properties of Gd-CQDs-4 were studied by UV-Vis absorption spectrum and fluorescence spectra.Gd-CQDs-4 showed obvious red fluorescence emission and exhibited a fluorescence quantum yield of 11.1%.RAW264.7 cells were selected as research objects,the cytotoxicity of Gd-CQDs-4 and the CLSM images within different uptake times showed that Gd-CQDs-4 has good biocompatibility and could be used in the field of fluorescence imaging.In addition,to further study the performance of Gd-CQDs-4 as a multimodal imaging probe,the longitudinal relaxivity?r₁?was measured to be 22.6 mM^-1s^-1.?3?On the basis of work?2?,the gadolinium-doped carbon quantum dots?Gd-CQDs?prepared in aqueous solution are combined with aminated Fe₃O₄nanoparticles to prepare T₁-T₂ type MRI/FI dual-modal probe Gd-CQDs@N-Fe₃O₄.The structural composition and surface morphology of Gd-CQDs@N-Fe₃O₄ were characterized by XRD,TEM,FTIR and XPS.The fluorescence and magnetic properties of Gd-CQDs@N-Fe₃O₄ were studied by UV-Vis absorption spectrum,fluorescence spectrum and VSM measurement.Gd-CQDs@N-Fe₃O₄ exhibited superparamagnetic behavior and a fluorescence quantum yield of 1.29%.To evaluate the potential of Gd-CQDs@N-Fe₃O₄ as a T₁-T₂ type MRI/FI dualmodal probe imaging probe,the relaxation performance of Gd-CQDs@N-Fe₃O₄ was studied.The longitudinal relaxivity?r₁?value and transverse relaxivity?r₂?value of Gd-CQDs@N-Fe₃O₄ were determined to be 5.16 mM^-1s^-1 and 115.6 mM^-1s^-1,respectively.