Functional Nanomaterial Optical Imaging Research Based On Single Molecule Spectroscopy

Recently, with the rapid developments in nanomaterial fabrication and characterization, lots of functional nanomaterials have been successfully utilized in biomedical applications. Due to their unique optical and chemical properties, those nanomaterials show new insights into high performance disease diagnosis and treatment. However, some grand challenges still exist. For example, how to realize ultrasensitive diagnosis (at single molecule or single cell level) for some major diseases? How to improve the biocompatibility of those nanomaterials? How to achieve the controllable fabrication of particular functional nanomaterials? To figure out these challenges, firstly, we need to develop new characterization method to explore the growth mechanism, the optical and physical properties of those new nanomaterials. Secondly, based on their excellent optical properties, to achieve ultrasensitive detection, we have to develop new detection strategies for those nanomaterials. Thirdly, to explore the interaction mechanism of those nanomaterials with biomolecules or to study the working mechanism of certain vital biological process with those functional nanomaterials, we need to build up high throughput techniques for those systems. In this article, we performed the research in the following three parts:(1) Based on differential interference contrast microscopy, we studied the self-assembly process of18nm gold nanoparticles at the air/water interface. From the single particle thermal diffusion results and nanostructure fractal dimension analysis, we found that this self-assembly process is neither diffusion controlled nor reaction limited but falls to an intermediate process between these two models. Meanwhile, the single particle tracking experimental results show that the key factor that controls the final morphology of the nanosubstrate is the electrostatic repulsion force between the nanoparticle and nanocluster. Since the electrostatic repulsion force on the side wall is much stronger than that on the terminal, the new adsorbed nanopartilces show a very high probability to attach on the terminal of the nanocluster which results in the final dendritic structure (Chapter2). We also developed a novel high throughput single molecule spectrum imaging method to characterize the luminescence mechanism and photophysical properties of new generation fluorescent probe, silver nanocluster. By inserting a transmission grating into the collection light path of a total internal reflection fluorescence microscopy, we can parallelly determine tens of fluorescence spectra from individual silver nanoclusters in a single image. With this method, we found that the laser induced silver nanoclusters on the silver island surface are neutrally charged and only three types of silver nanoclusters exist on the surface when induced by488argon ion laser. Similar to the dye molecules, they also have blinking phenomenon and the fluorescence intensity can be greatly enhanced by neighboring silver islands (Chapter3).(2) Through total internal reflection fluorescence microscopy, we studied the interaction mechanism between CdTe quantum dots and amyloid peptide in detail. From the experimental results, we found that the self assembly process of amyloid peptide can be finely regulated by quantum dots. Due to the strong hydrogen bond between quantum dots and amyloid peptide, the quantum dots can tightly bind onto the growth sites of the amyloid fibril. As a result, in the presence of quantum dots, the aggregation process can be effectively inhibited. This mechanism was confirmed by computer simulation. Moreover, based on the above assumption, we derived the kinetic reaction equation and we found that this model fitted well with experimental results. The information obtained at here would provide a new avenue for the treatment of Alzheimer’s disease with functional nanomaterials (Chapter4). In order to realize ultrahigh detection sensitivity on human disease, we developed a colorimetric detection strategy with gold nanoparticles as the probe molecule. This method is based on the plasmon resonance coupling effect between two neighboring40nm gold nanoparticles. Once two nanoparticles were pulled together closely, the resonance scattering peak of the dimer would shift into red region. With this technique, we successfully detected the breast cancer related DNA sequence at single molecule level and we also demonstrated that this method can be applied in multiplexed ultrasensitive analysis (Chapter5).(3) In order to utilize the promising nanoparticles as a probe molecule for some vital biological process, we developed two optical imaging methods for orientation measurement. Since the scattering light from single gold nanorod is anisotropic, it could be treated as a local orientation sensor in nanoscopic system. For the first time, we successfully used the defocused dark field image to deconvolute the three dimensional orientation of single gold nanorod on the glass slide surface (Chapter6). Meanwhile, we built up another planar illumination microscope for fast rotational dynamics tracking. With this method, we directly visualized the rotational dynamics of motor protein on microtube inside living cell (Chapter7).