The Regulation Of LSPR Characteristics Of Nano-dendritic Gold And Its Application In Tumor Photothermal Therapy

In recent years,cancer has become a major killer of human life,so finding a fast and effective way to diagnose and treat cancer has become an active target for the medical community and the entire scientific community.Near-infrared photothermal therapy,as a new type of cancer treatment,has attracted widespread attention.It is mainly to use photothermal reagents to convert light energy into heat energy to kill cancer cells,thereby reagents plays a very important role throughout the photothermal process.The commonly used photothermal reagents mainly include photosensitive materials and nano materials.Among them,gold nanomaterials have attracted the attention of researchers due to their unique local surface plasmon resonance characteristics(LSPR).Therefore,it has a wide range of applications in various aspects such as disease diagnosis and treatment and biological imaging due to the flexible and adjustable LSPR characteristics.In addition,gold nanomaterials also have good biocompatibility,which is also the basis of its application in the biological field.However,how to adjust the LSPR characteristics of gold nanoparticles to design and prepare gold nanoparticles with high photothermal conversion performance is still an urgent problem to be solved.Therefore,this dissertation aims to clarify the relationship between the LSPR effect of gold nanoparticles and its structural parameters by means of Finite-Difference Time-Domain theory(FDTD),and then screen out the special microstructure characteristics with high photothermal through theoretical simulation prediction.And then the gold nanoparticles were synthesized experimentally and finally applied to the photothermal therapy of cancer.The main research contents of this thesis are as follows:(1)Theoretical simulation of LSPR characteristics of gold nanoparticles,and the preparation and photothermal conversion performance of gold nanoparticles.First,we constructed a simple model of a single gold nanosphere and a gold nanorod,and predicted the LSPR characteristic peak and its field strength.The simulation results show that for gold nanospheres,the LSPR characteristic peak cannot reach the near-infrared;for gold nanorods,the field strength is only strong at the tip.Therefore,gold nanospheres and gold nanorods are not suitable for photothermal treatment of tumors.On this basis,we constructed multibranched gold nanoparticles(M-AuNPs)with different structural parameters(different number of branches,length of branches and core size)with gold nanospheres as the core and gold nanorods as the branches,and predicted the LSPR characteristics,the absorption cross section(Cabs)and the absorption cross section to the scattering cross section at a wavelength of 808 nm(Cabs/Csca).Finally,by adjusting various structural parameters,it is found that when the number of branches of M-AuNPs is 5,the branch length is about 40 nm(the aspect ratio is about 2),and the core size is about 25 nm,they have high Cabs and Cabs/Csca at 808 nm(?4.2 × 10-14 m2,?3.0),and strong field strength in each source and polarization direction.On the basis of theory,M-AuNPs with different structural parameters was synthesized by seed-mediated growth method and characterized by various characterization methods(TEM,UV-Vis,etc.).The Cabs/Csca of M-AuNPs with different structural parameters were calculated by the photoacoustic imaging signals at 808 nm,and found that it is basically consistent with the theoretical simulation values,such as when the number of M-AuNPs is 5 and the length of branch is about 40 nm(length to diameter ratio is about 2)and the core size is about 25 nm,the Cabs and Cabs/Csca are(2.4 ± 0.1)× 10-14 m2 and 3.0 ± 0.1,respectively;further,for different structural parameters of M-AuNPs,the photothermal properties of AuNPs were investigated.It was found that when the number of branches was 5,the branch length was about 40 nm,and the core size was 25 nm,the photothermal conversion efficiency was the highest(about 56%),which was in good agreement with the theoretical results.(2)Application of gold nanoparticles in vitro photothennal therapy of human breast cancer cells(MCF-7)and photothermal therapy in mice in vivo.Firstly,the results of MTT assay showed that the M-AuNPs was not cytotoxic,so it could be safely used for photothermal therapy of cancer.Then the M-AuNPs was used for near-infrared photothennal therapy of MCF-7 cells,and a large number of deaths occurred in MCF-7 cells after therapy.Finally,the M-AuNPs was used for near-infrared photothermal therapy of breast cancer mice.After therapy,the tumor site of the mice became significantly smaller and the physiological phenomena of the mice were still normal.Furthermore,the mechanism of death of cancer cells was also studied,and it was found that the cells mainly died of necrosis during the therapy.Therefore,this work provides a theoretical basis for the adjustment of LSPR characteristics of gold nanoparticles and preparation of gold nanoparticles,and also shows that M-AuNPs have a good application prospect as a photothermal therapy reagent for tumors.