Construction Of Polyamino Acid Mediated Gold Nanostars And Photothermal Therapy Research

Gold nanostar(AuNS)is a kind of anisotropic gold nanoparticles with multibranch structure,whose optical properties can be changed with the length and number of branches,and size of the particles.In recent years,AuNS has been playing an important role in biosensing,photothermal therapy(PTT),surface-enhanced raman scattering,and so on.The prevailing methods of AuNS preparation are seed-mediated and one-step synthesis methods,and the toxic cetylammonium bromide or polyvinylpyrrolidone is often used as the surfactant.In this thesis,AuNS is prepared by seed-mediated,template-based and one-step synthesis methods using poly(y-glutamic acid)(y-PGA)instead of conventional surfactants,and its photothermal properties are investigated.The details of the study and the conclusions are as follows:1.Seed-mediated method for preparation of AuNS(S-AuNS).PGA and polyacrylic acid(PAA)modified Fe3O4 are prepared as seeds by co-precipitation method using y-PGA and PAA,respectively.AuNS is prepared by adding the seeds to the growth solution of gold.In this section,the effects of the concentration of y-PGA and PAA in seeds on the morphology and near-infrared absorption spectra of S-AuNS are investigated.It is found that the use of y-PGA or PAA to prepare the seeds is eventually able to obtain gold particles with star morphology,but their large size(about 500 nm)affects their application in photothermal therapy.2.Template method for preparation of AuNS(T-AuNS).In this method,poly(?-lysine)(PL)and y-PGA are firstly encapsulated on the surface of nonporous silica nanoparticles(MSN)by layer-by-layer self-assembly technology.The MSN with the outermost layer of y-PGA as a template(MSN@PL/PGA)is used to prepare T-AuNS.The T-AuNS has obvious absorption peaks in the Near-infrared radiation(NIR)range,but the number of branches is small and the length is short.It is assumed that the chloroauric acid(HAuCl4)is adsorbed on a small amount of free y-PGA and does not grow on the MSN@PL/PGA.The experimental results of the seed-mediated and template-based methods demonstrate the key role of y-PGA in the formation of the star-shaped morphology3.One-step synthesis method for preparation of AuNS(O-AuNS).This method uses a solution containing y-PGA to prepare the growth solution of gold,and adds the reducing agent to directly reduce HAuCl4 to obtain O-AuNS.In this part,the effects of the concentration of each reactant and the pH of the solution on the particle morphology and NIR absorption spectra are investigated.The optimized results are 1 mg/mL y-PGA,24.13 mM HAuCl4,445 mM NH2OH·HCl,and pH 7.3.The O-AuNS obtained under these conditions has a good morphology and homogeneous size(about 200 nm),with strong near-infrared absorption.4.O-AuNS has light-enhanced peroxidase(POD)activity and excellent photothermal performance with a photothermal conversion efficiency of 36.5%.At the cellular level,O-AuNS has good biocompatibility.Under the irradiation of near-infrared light(808 nm,2 W cm-2),200 ?g/mL of O-AuNS could kill 71.09%of tumor cells,which demonstrates the effect of therapy.In summary,in this thesis,AuNS is prepared by three different methods using y-PGA instead of surfactant,and the final results demonstrate that the one-step synthesis method is simpler and greener than the seed-mediated and template-based methods with complicated steps,and O-AuNS has a better morphology and smaller size.Meanwhile,At the cellular level,POD activity improves the killing effect of PTT on tumor cells.