Optical Properties Of Nanocrystals And Their Applications In Biological Imaging And Single Molecular Tracking

Nanocrystals have a broad application prospect due to their unique optical properties. Biological labeling and imaging is one of the most promising applications for nanocrystals. Semiconductor nanocrystals or quantum dots, and noble metal nanocrystals are the main classes of nanocrystals.This thesis aims to design and synthesize quantum dots and gold nanorods, study their optical properties and cytotoxicity, apply them for biological labeling and imaging, and single biomolecule tracking.Quantum dot is a rapidly booming fluorescent probe in recent years. Herein we have developed two types of high quality water-soluble quantum dots for bioimaging application. They were MSA-capped CdTe/ZnSe quantum dots synthesized by an aqueous method and MSA-capped CdTe quantum dots by hydrothermal method. Their emission can be tuned from green, yellow, orange till red. Meantime, these two quantum dots have many merits such as high fluorescence quantum yield, narrow full width of half maximum of fluorescence peak, high photo-and pH-stability and low cytotoxicity. Both quantum dots were conjugated with immunoglobulin G forming fluorescent probes, and labeled the cancer marker HER2on the MCF-7cell membrane for imaging.The fluorescence blinking of single quantum dots would lead to information loss during dynamic tracking. We have studied the blinking phenomenon and the mechanism behind. We found that two nearby quantum dots were likely to blink synchronously, or to say fluorescence blinking bunching effect. The long-range Coulomb interaction for charged quantum dots was probably the cause for blinking in single quantum dots and the bunching effect in quantum dot pairs.Along with the nanocrystals are gradually extensive in many fields, the impact of nanocrystals on human beings and biological environment cannot be discounted. The cytotoxicity for CdTe quantum dots were studied with human umbilical vein endothelial cells as an in vitro model. The experimental results implied that CdTe quantum dots induced cell apoptosis through a mitochondrial apoptotic pathway. This pathway including several processes such as cell membrane phosphatidylserine translocation, intracellular reactive oxygen species level increase, mitochondria dysfunction, cytochrome c release, caspases activation and so on. Nevertheless drug treatment could cut off or relieve the apoptosis process and protect the cell.Gold nanoparticles can be used as scattering probes for biological labeling and imaging based on the surface plasma resonance enhanced scattering properties of gold nanoparticles. In order to obtain gold nanorods with high yield and uniform morphology, we have systematically studied the influence of the concentrations of CTAB and silver ions to the quality of gold nanorods produced via the seed-mediated method. Results indicated that the morphology and yield of nanorods produced were effectively controlled by adjusting the molar ratio of CTAB to silver ions. The as-produced high quality gold nanorods were nonspecifically stained COS-7cells for dark field scattering imaging.The last part of this thesis is exploratory research on diffusion and interaction of biological molecules at the molecular scale. On one hand, Considering the permittivities of silver and PMMA are matched at365nm, silver superlens produced basing on the mechanism of negative-index imaging overcame the diffraction limit. However this imaging method so far is so critical to the samples that can hardly extend to live cell imaging. On the other hand, quantum dots were conjugated affibodies, which are novel artificial antibodies, to produce fluorescent bioprobes. This kind of probes was stained to single HER2molecules on the membrane of A431epidermoid cancer cells. Single molecular tracking was performed for the live cells to study the diffusion coefficient of the single molecules, size of transient confinement zones, interaction modes of the molecules and the transient confinement zones, and so on.