| With the continuous advancements in nanoscience and nanotechnology, noblemetal nanoparticles with unique physical and chemical properties, which attractedmore and more interests of scientific researchers, have been widely applied in variousareas such as biochemistry and life sciences. As optical probes, metal nanoparticlessuch as gold and silver nanoparticles, possess of many advantages comparing withother traditional optical probes, such as high photostability, large opticalcross-section, easy to prepare and modify, well biocompatibility. Thus, noble metalnanoparticles displayed promising prospects in the applications of chemical analysisand biological sensing, biomedical and bioimaging. Based on the optical properties ofmetal nanoparticles, single-particle imaging and single-particle spectroscopy withnanometer-scale spatial resolution and millisecond time resolution have becomeimportant means for studying the behaviors and functions of biomolecules atsingle-cell level. Due to high surface chemical activities, metal nanoparticles havealso been used as active nano-catalyst for the catalysis in chemical engineering andenvironmental protection, biochemistry and biomedicine. However, there are stillgreat challenges we have to meet during various applications of metal nanoparticles,such as the declining in detection sensitivity due to the polydispersity of particle sizeand morphology, lower selectivity and temporal-spatial resolution of current methodsfor detecting in biological environments, etc.Based on the existing research, we setted out to provide some solutions for theproblems and challenges in previous studies and the main points of our work in thisthesis are summarized as follows:(1) A new kind of method has been proposed for the purification ofnanoparticles by using density gradient centrifugation. On the basis of force balanceof steady sedimentation, we have deduced the expressions of sedimentation rate ofnanoparticles with different sizes and shapes. By using the rate difference in thedensity gradient centrifugation, gold nanorods with differents aspect ratios has beensuccessfully isolated and purifed. To improve the separation efficiency, the effect ofcomposition of gradient solutions and centrifugation time were studied in ourexperiments. Both experimental results and calculated results demonstrated that,although particles can not be sperated for some special cases, density gradient centrigugation is still an effective method for the separation of nanoparticles withdifferent shapes and sizes.(Chapter2)(2) The unique optical properties of gold nanorods were systematically studied.The locallized surface plasmon resonance (LSPR) absorption and scattering of goldnanorods can be calculated according to Gans theory. In this section, the expressionfor the relationships between spectral shifts and refractive index changes of mediumsolution was derived based on the resonance conditions of gold nanorods. Theexperimental results show that, the spectral redshift of gold nanorods linearly scaledup with the increase of refractive index of the medium solution, and the sensitivity ofspectral is related with the aspect ratios of gold nanorods. These results arecompletely consistent with the calculated results. In addition, we also investigatedthe factors which can affect the accuracy of single-particle detection.(Chapter3)(3) Detection of sulfide with high sensitivity and selectivity was achieved byusing conventional UV-visible spectroscopy and single-particle spectral microscopywith gold-silver core-shell nanorods as probes. The gold-silver core-shell nanorodswere highly selective towards sulfide than other chemical species due to ultralowsolubility of Ag2S (pKsp=50.83). Two linear ranges from0.1μM to1mM and from0.01nM to10μM were obtained by using UV-visible spectroscopy andsingle-particle spectroscopy, respectively. The limit of detection of single-particledetection is much lower than by UV-visible spectroscopy, which implies thedetection at single-particle level a much sensitive than that of bulk measurements.(Chapter4)(4) From the study of reaction kinetics between the gold-silver core-shellnanoprobes and sulfide, we successfully measured the local concentrations ofhydrogen sulfide (H2S) and its oscillation in live cells by monitoring the spectralredshift of nanoprobs. A relationship between the reaction kinetics and shifting rateof the spectra of single nanoprobes has been established. Then the time-dependentspectral shifting curves were obtained both experimentally and theoretically when thenanoprobes were exposed to different concentrations of sulfide solutions.By usingthese curves as external calibration curves, the variations of local H2S concentrationin live cells can be determined throuth detecting the LSPR spectral of singlenanoprobes in real time.With this method, generation of endogenous H2S in live cellsby applying external stimulation were detected with the nanoprobes.(Chapter5)(5) Using the astigmatism phenomenon induced by a cylindrical lens, we havedeveloped a three-dimensional dark-field imaging techniques with gold nanoparticles as optical probes, and tracked the three dimentional diffusion of gold nanoparticles inthe solution. The direction of particle diffusion can be distinguished accuratelyaccording to the changes in the length of two axis of scattering spots. Comparingwith existing methods for three-dimensional imaging, a much higher vertical spatialresolution (~70nm) was obtained and the three-dimentional diffusion coefficients ofmoving gold nanoparticles have been measured in our experiments.(Chapter6)(6) Highly active gold-platinum nanocomposites (Au-Pt NPs), which cancatalyze the decomposition of hydrogen peroxide, superoxide anion and otherreactive oxygen species, have been prepared with seed mediated growth method. TheAu-Pt NPs can be readily uptake by human skin cells after surface modification. Theresults of cell cytoxicity indicated that the Au-Pt NPs are well biocompatible, andalso the Au-Pt NPs can remarkably reduce cellular oxidation stress after treated withhydrogen peroxide. This propertiy was used for scavenging cellular reactive oxygenspecies and protecting from UV Irradiation induced cell damages in our study.(Chapter7)... |
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