The Research Of High Resolution Plasmonic Imaging With Single Gold Nanoparticle

With fast development of nanoscience and nanotechnology, the localized surfaceplasmon resonance (LSPR) metal nanoparticle have been selected to be molecularprobe for study time consuming biology process due to its photo stability. Because oftheir unique optical, chemical and biological properties, metal nanoparticles (MNPs)have attracted considerable attentions in biomedical science. To evaluate the surfacechemistry and performance of MNPs as potential disease diagnosis and drug deliveryagents, plasmonic imaging techniques dare often required to investigate real-timeMNP interactions with cells/tissues and their spatial-temporal distributions insidebiological specimens. However, there are still some grand changes. For example, howto selectively image metal nanoparticle in noisy living cells? How to detect andresolve nanometer-sized objects at spatial resolution below the optical diffractionlimit? How to improve axial resolutions to reconstruct the metal nanoparticle3Ddistribution in cells? How to amplify small color difference between goldnanoparticles in colorimetric analysis?Based on previous research work, we attempt to figure out the above problemsand the main points of this thesis are summarized as follows:(1) Through differential interference contrast (DIC) microscopy, we developed anew optical imaging method to selectively distinguish the metal nanoparticle insidesthe living cells with illumination of RGB lasers. Based on their unique opticalproperties, it has been demonstrated that the Plasmon nanoparticles have goodcontrast near their plasmon resonance (PR) wavelengths. By shaking the fibers,interference fringe could be effectively eliminated and distinct images could beachieved under laser illumination. Exploring the DIC images of4kinds ofnanoparticles immobilized on cover glass respectively, the unique DIC contrastspectrum was established. By using the spectrum as calibration curves, the goldnanoparticle and Au/Ag/Au nanoparticles were simultaneously discriminated andimaged. This simple method could be potential be used to study the diffusiondynamics of nanoparticle on the cell membrane and the interaction of nanoparticlewith cell membrane.(2) Based on the imaging principle of cross-polarization microscopy, a new kindof imaging technique was developed to selectively image the anisotropic goldnanorods. Compared with the imaging results of different size of gold nanoparticles and gold nanorods, this method had been proved to specifically image the goldnanorods, while it cannot distinguish gold nanoparticles. By rotating the samplerelative to the polarization of the illumination light, it can be seen that the intensity ofsingle nanorod change periodically. The spatial resolution of cross-polarizationmicroscopy are better than that of dark field microscopy due to a high numericalaperture objective. By regulating the thickness of the silica shell to minimizethe inter-particle plasmonic coupling, optical encryption application could beachieved. This imaging technique could be applied to fingerprint optically anisotropicmetal nanoparticles and their assemblies for labeling, sensing, and encryptionapplications.(3) By exploiting the orientation-dependent LSPR scattering properties of singleAuNRs under cross-polarization microscopy with a high NA objective, we havedemonstrated subdiffraction-limited imaging of plasmonic MNPs. Taking advantageof their anisotropic optical property of the plasmonic scattering of AuNRs, selectiveimaging of only a fraction of AuNRs can be achieved by rotating the sample relativeto the linear polarized illumination under cross-polarization microscopy with a highNA objective. The AuNR positions obtained from a series of images could then beused to reconstruct the overall image. Two AuNRs with center-to-center distances of80nm were successfully resolved. This simple and high-resolution plasmonic imagingtechnique could be widely used in many areas in physical, chemical, biomedical, andmaterial science.(4) By using cross-polarization microscopy and a high NA objective, selectiveimaging of gold nanorods could be achieved not only at the x-y plane by rotating thesample horizontally but also along the z-axis by scanning the sample vertically. Byexplore the point spread function of gold nanorods immobilized on glass slides in they-z-plane obtained at an axial step size of69nm using the cross-polarizationmicroscopy, it is concluded that one possible explanation to such an optical effect ishigh NA objective induced spherical aberration. In order to study the interactionbetween gold nanorod and cell using the method, we replace the CTAB with MTAB toprotect gold nanorods which had low cytotoxicity and high cellular uptake. Theselective imaging results indicate that this method could be used to study the kineticinformation of the internalization process.(5) Samples with small spectral variations often cannot be differentiated in colordue to the nonlinearity of color appearance, we address this problem by exploiting thecolor image formation mechanism in digital photography. A close examination of the color image processing pipeline emphasizes that although the color can be representeddigitally, it is still a reproducible subjective perception rather than a measurablephysical property. Then to extract the intensity-independent chromaticity values fromstandard gamma-encoded sRGB images, a calibration based method is established. Weexpect this strategy to be widely used for colorimetric sensing in various fields.(6) In order to amplify the small color difference between gold nanoparticles incolorimetric analysis, we replace the conventional spectrally continuous white lightwith spectrally discrete, independently intensity-controlled narrow-band light sources.By using scattering light imaging of gold nanoparticles (GNPs) as a model system, wedemonstrated via simulation that enlarged color difference between spectrally closesamples could be achieved with actively controlled illumination of multiplenarrow-band light sources. Experimentally, darkfield imaging results indicate thatcolor separation of single GNPs with various sizes can be significantly improved andthe detection limit of GNP aggregation-based colorimetric assays can be muchreduced when the conventional spectrally continuous white light was replaced withthree independently intensity-controlled laser beams, even though the laser lines wereuncorrelated with the LSPR maxima of the GNPs. With low-cost narrow-band lightsources widely available today, this actively controlled illumination strategy could beutilized to replace the spectrometer in many spectral sensing applications.