Localized Surface Plasmon Resonance Modulation And Photothermal Therapy Application Of Gold/Silver Nanoparticles

Noble metals,such as gold and silver,have significant local surface plasmonic resonance(LSPR)property,which makes the surface of nanocrystals produce a strong local electric field,indicating a wide range of applications in the fields of surface enhanced Raman scattering,fluorescence,biosensors,imaging,photothermal therapy and catalysis.Among noble metal nanomaterials,silver nanoparticles have excellent resonance properties in the spectral range of 300 nm to 1200 nm.However,due to their poor biotoxicity,chemical stability and physical stability,their applications in related fields in vivo are limited.On the other hand,gold nanoparticles have low cytotoxicity and good chemical and physical stability,so they are suitable for biological applications.However,the coupling between the interband transition and local surface plasmon resonance,gold nanoparticles exhibit superior LSPR properties only when the wavelength range is greater than 500 nm.Aiming at these problems,this paper mainly focused on the modulation of the LSPR effect of gold/silver nanoparticles through two ways.One is to change the environmental medium of nanoparticles by using thermosensitive phase-change materials to modulate the scattering spectrum actively,which was adjusted by external temperature.The other is to change the morphology and composition of those nanoparticles for the shift of the absorption peak of the material.Because of the most effective photon-to-phonon conversion(as well as the highest photothermal conversion efficiency)when the absorption peak of the plamon matches the excitation wavelength.They were finally used in the detection of cation and ions,photothermal therapy and antibacterial applications.The specific work is detailed as follows:(1)Considering it is difficult to combine gold and vanadium dioxide directly through chemical synthesis due to the mismatch of crystal lattice,the monodisperse vanadium dioxide particles with gold caps were prepared by a combination of physical and chemical methods.Monodispersed hybrid Au-VO₂ nanoparticles has been synthesized and optically characterized.Compared to standard noble metal particles,these Au-VO₂ nanoparticles exhibit an additional reversible tunable LSPR under external temperature stimuli.The LSPR wavelength of the single hybrid nanoparticle shifts reversibly from 546 nm to 755 nm when the temperature changes from 25?to90?.Such a smart and very large modulation(more than 200 nanometers in wavelength)can be attributed to unique insulator/metal phase transition of VO₂particles.The simulation result using the finite-difference time-domain(FDTD)method is consistent with experimental data.(2)Based on crystal seed growth method,a batch of silver-gold core-shell nanotriangles were prepared and used as a kind of nano-probe to realize highly sensitive and selective detection of mercury ions and sulfur ions.The detection of mercury ions was based on the formation of silver amalgam,and the detection of sulfur ions was based on the rapid reaction of sulfur ions with silver atoms to produce silver sulfide in the presence of oxygen at room temperature.All of the above resulted in a significant shift in the position of the absorption peaks measured by UV-Vis spectra,and with the great change in the color of the solution,it could be identified with the naked eye.The ion detection limitation reached 10 n M and 20 n M,respectively.The purpose of visual trace colorimetric detection was realizied.(3)Through introduction of sulfite ions,the silver nanoplates were protected from the galvanic replacement with gold,thus the Ag@Au nanoplates were successfully prepared.The Ag@Au nanoplates was used for photothermal therapy and enhanced the function of computed tomography(CT).During the process of synthesis,the absorption peak was moved by adjusting the size of the silver nanoplates,and then the surface of the silver nanoplates was coated with a layer of gold,which not only improved the stability of the nanomaterial,but also reduced the cytotoxicity of the nanoparticles,so that it could meet the requirements of treatment in vivo.Furthermore,the high atomic numbers of both Ag and Au elements made the nanoplates promising contrast agents for computed tomography that can be harnessed to guide the tumor ablation.Through in vitro and in vivo experiments,the effectiveness and biocompatibility of the Ag@Au nanoplates as a good photothermal therapy agent were proved.(4)The Ag@Au nanoparticle were further oxidized to form surface holes.The resulting p-Ag@Au nanoparticle could effectively deal with the wound infection of Staphylococcus aureus.In the experiment,the 808 nm laser was used to irradiate the nanoplates.On the one hand,its excellent photothermal effect could effectively destroy bacterial organisms.On the other hand,as the temperature rised,silver ions were further released through surface holes to improve antibacterial performance.Comparing with Ag nanoplates,the irradiated porous Ag@Au nanoplates showed the similar antibiotic ability against S.aureus strains and lower cytotoxicity in vitro.When the porous Ag@Au nanoplates were applied to treat S.aureus-infected wound,they had the best curing effect.Thus,these porous Ag@Au nanoplates could act as promising antibacterial agents for wound healing applications.