Optical Properties Regulation And Optical Microscopic Imaging Of Gold Nanoparticles

Metallic nanomaterials have played an important role in various fields.In recent years,to investigate the interaction between individual particles and the surrounding environment in real time and in-situ is the development trend of nanotechnology.As one of the most commonly used nanomaterials,gold nanoparticles have become a research hotspot because of its simple preparation,good stability and strong scattering performance.They are widely applied in materials science,optics,sensing,biomedicine and so on.In this paper,two kinds of gold nanoparticles(spherical gold nanoparticles(GNPs)and gold nanorods(GNRs))were used to study the local surface plasmon resonance(LSPR)characteristics by optical microscopy.This thesis includes the following three sections:(1)Tuning plasmon resonance in-situ in a single spherical GNP during incident laser melting was studied.A beam of laser(532 nm)was focused on a selected particle,its optical properties and shape changes could be observed by dark field microscopic imaging system.It was found that 60 nm GNP gradually transformed from a sphere into an ellipse along with laser irradiation.The plasmon resonance spectra moves in a certain range and could be tuned by adjusting the time and intensity of the incident laser.In addition,after the incident laser irradiation,the polarization of the particles was closely related to the polarization of the laser,meanwhile,significant fluorescence enhancement of GNP was observed.These results would provide a good reference for people to preferably understand the local surface plasmon resonance,and to further develop the plasma exciton system with directional oscillation.(2)With wavelength-resolved dark-field microscopy,the center-of-mass localization information from nanoparticle pairs(i.e.,spherical and rod shape gold nanoparticle pairs with different gap distances and orientations)was explored and compared with the results determined by scanning electron microscopic(SEM)measurements.When the gap distance was less than 20 nm,the scattering spectrum of the nanoparticle pair was seriously modulated by the plasmonic coupling effect.The measured coordination information determined by the optical method(Gaussian fitting)was not consistent with the true results determined by SEM measurement.A good correlation between the optical and SEM measurements was achieved when the gap distance was further increased(e.g.,20,40 and 60 nm).Under these conditions,well-defined scattering peaks assigned to the corresponding individual nanoparticles could be distinguished from the measured scattering spectrum.These results would afford valuable information for the studies in single plasmonic nanoparticle imaging applications with optical microscopic method such as super-localization imaging,high precision single particle tracking under crowding environment and so on.(3)A new strategy,total internal reflection scattering(TIRS)microscopy,was developed to determine the full three-dimensional(3D)angular information on a single GNR close to the liquid/solid interface.It was found that the 3D orientational information on individual GNR could be readily elucidated by using p-polarized TIRS illumination through deciphering the orientation-coded intensity distribution pattern in a single TIRS image.In comparison with the previously reported strategies,this method does not require complicated focal plane correction,affording a versatile pathway to track the rotational dynamics close to the interface in a high throughput manner.The methodology presented here,therefore,demonstrates a promising approach that can be applied to anisotropic nanomaterials and fluidic membranes.