Synthesis Of Monodisperse Gold Nanorods And Application Of Imaging Methods

Biology researches have shifted from studying common characteristics of groups, to individual differences among a group, then to how these differences affect the whole group. To study these differences, single molecule detection technique has gradually become a necessary means in routine experiments. This technique focuses on investigating behaviors of single molecules, single cells, or specific functional biomolecules in a single cell in order to resolve the complex and highly coordinated life mechanisms of organisms. In most single molecule detections, fluorescent dyes are very useful probes. However, in single molecule detection in living cells, the intensity of signals that dyes provide is not adequate to be detected. So it is greatly needed to develop new probes with potential application in detecting the mechanisms of biological molecules in single living cells. Noble metal nanomaterials with surface plasmon resonance have received great attentions since they were initially synthesized. There is a large pool of literature that reported the application of these nanomaterials as probes and drug carriers in biological systems. With the study progress of noble metal nanomaterial, single molecule imaging technique using noble metal nanoparticles has also developed quickly. Here, we study new imaging methods of single gold nanorods, which is mainly to be discussed in the following three aspects:(1) Selective imaging gold nanorods using Polarization MicroscopySelective imaging of anisotropic nanoparticles can be realized with polarizing microscopy and three dimensional scanning of sample using objective with high numerical aperture. With high NA value, the depth of field of the objective is thin, so the axial sectioning of sample is possible when moving objective vertically. Therefore, by coupling polarization microscope with an objective with high NA, it is capable to achieve three dimensional imaging of anisotropic nanoparticles. Gold nanorods are relatively simple anisotropic nanomaterial. Their optical properties are stable and they can be modified with a variety of biological ligands, so they are suitable probes to study activities in single cells.(2) Synthesis of gold nanorods with intense scattering and light polarization dependence of scattering signalsFor gold nanorods with a constant diameter, an increase in their aspect ratio would not result in any considerable increase of their extinction cross-section values. While for gold nanorods with the same aspect ratio, larger diameter would result in more surface electrons, stronger surface plasmon resonance effect, as well as stronger scattering signals. Gold nanorods, which are synthesized using seed mediated method, are allowed to overgrow without silver nitrate during the growth process so that their long axis would not become their major growth direction. In this way, we can obtain gold nanorods with diameter of about 30～40nm, and length of about 70nm. Is has been demonstrated that the scattering light of these anisotropic gold nanorods is strongly polarized along their long axis, making them in principle perfect orientation probes for single molecule experiment. The intensity of scatterring light is strongly dependent on the square of the cosine of the relative angle between the long axis and the polarization light. Dark field condenser changes the polarization direction of the incident light, making the polarization directions different. Therefore, we cannot obtain pure scattering signals along the short axis of gold nanorods even if the polarization direction is perpendicular to the long axis of gold nanorods. Also, the trend of gradual color change between read and green is not observed.(3) Imaging of translational and rotational diffusion of gold nanorods in cells using planar illumination microscopy.According to the similar theory of polarized fluorescence imaging, we can divide the imaging process of gold nanorods into two parts: absorption and scattering, which are both associated with the spatial angles of the gold nanorods. In detail, samples are illuminated with planar polarized light, and by passing through Wollaston prism, their scattering signals are divided into two polarized lights, which are mutually perpendicular. We can obtain the spatial angles of the gold nanorods by detecting the intensities of the signals of the polarized lights from the two channels. We also study the effect of surface modifications and the impact of the solution viscosity on the rotational dynamics of gold nanorods. We find that in a single cell, the trajectory of gold nanorods is different, accompanying with their own rotating movement.