Synthesis Of Boron Doped Carbon Dots With Optical And Magnetic Properties

Fluorescence and magnetic resonance(MR)are vital techniques in the fields of biology.To date,heavy metal ions-based materials have been used as probes for dual mode imaging.However,heavy metal ions are not friendly to environment and organism.Therefore,finding a metal-free bimodal probe is of great important.Carbon dots have been widely used in bioimaging because of their excellent biocompatibility,fluorescence tunability,photobleaching resistance and high sensitivity.Nowadays,the preparation of carbon dots with fluorescence and magnetic resonance properties focus on the strategy of heavy metals doping,especially gadolinium,which can inhibit calcium channels,cause cardiovascular and neurologic toxicity.Therefore,the development of metal-free doped carbon dots with fluorescence and magnetic resonance dual-mode imaging has also become a hot spot in this field.In this paper,the boron-doped carbon dots have the functions of dual-mode imaging by designing the surface functional groups of carbon dots and doping atoms.In addition,the effect of nitrogen on the effective magnetic center during co-doping was discussed.As well as research on quench-resistant solid-state fluorescence and room-temperature phosphorescence,the specific work is as follows:1.Metal-free boron-doped carbon dots(B-CDs)with fluorescence and magnetic resonance dual-mode imaging were synthesized by a simple solvothermal method.Compared with boron-free carbon dots,B-CDs showed significant green fluorescence with up to 58.5%fluorescence quantum efficiency and a higher longitudinal relaxivity than commercial contrast agents(r₁=5.13 m M^-1s^-1).This indicates that boron doping can enhance the fluorescence intensity of the carbon dots and facilitate the expression of the magnetic center.The viability of He La cells after co-incubation with B-CDs was assessed by the standard MTT assay,and the results demonstrated that B–CDs exhibit low toxicity to He La cells.Histological analysis showed that the B–CDs had good biocompatibility and had little damage to the tissues of nude mice.Finally,fluorescence and magnetic resonance dual-mode imaging of B-CDs have been successfully applied in mice.Because of the simple preparation process,low cost,good biocompatibility and low toxicity of B-CDs,it is of great significance in molecular imaging research.2.Boron-nitrogen co-doped fluorescent carbon dots(B,N-CDs)were prepared by simple hydrothermal synthesis using p-carboxyphenylboronic acid,ethylenediamine and hydrogen peroxide as reaction precursors,which have fluorescence adjustability,low toxicity and good magnetic resonance imaging performance.Studies showed that boron doping causes the red shift of carbon dots emission peak and magnetic signal enhancement,and the introduction of ethylenediamine enhances the water solubility of carbon dots and also has a certain influence on the expression of effective magnetic centers.It demonstrated that the boronic acid group on the surface of the carbon dot is more favorable for the reverse recovery of the ¹H signal.In addition,B,N-CDs have quench-resistant solid-state fluorescence performance,and the fluorescence quantum efficiency reaches 7.10%at 468 nm excitation.B,N-CDs have a room temperature phosphorescence effect at 254 nm excitation,and the life curve can be fitted to a double exponential function,which means that there are multiple energy level transitions on the surface of the carbon dots,and the average lifetime is 237.07ms.Moreover,we also found that the afterglow imaging can be regulated by the concentration of carbon dots.