Preparation And Application Of Functional Gold Nanomaterials And Optical Microscopic Imaging Technology Development

Recently, functional nanomaterials (e.g. carbon nanotubes, silica nanowires, noblemetal nanostructures and so on) have received great attention in physics, chemistry andbiology. Among those nanomaterials, the gold nanostructure has become a “hot-spot”due to its unique photo-physical properties. Along with the enormous exploration ofnew synthesis and characterization methods, variety of novel gold nanostructures withdifferent shape and size have been synthesized and they are playing important role incatalysis, biosensing, optical imaging, biomedicine and so on. Despite their significantapplications, some important questions have to be addressed in advance before theirfurther usage in these areas. For example, how to improve the drug-loading efficiencywhen they are served as functional nanocarrier? How to control the colloidal stabilityin physiological solutions? How to elucidate the interaction mechanism between goldnanostructures and cellular membrane for the improvement of translocation efficiency?How to discriminate the target nanoparticle from the interfering signals inside livingcells? In order to provide insightful information to these questions, we have to developrobust and convenient methods for the characterization and exploration of thosedynamic processes at single nanoparticle level with high spatial and temporalresolution. In this regard, we performed extensive researches as described in thefollowing four parts:(1) Firstly, we synthesized gold nanoparticles with different size (18nm,40nmand60nm, gold nanospheres) and shape (gold nanorod). Due to the extremely largescattering cross-section at the plasmon resonance frequency, the scattered light willrepresent distinct color when illuminated by white light. Therefore, these nanoparticlescan be adopted as efficient imaging contrast agent based on scattering detectionmodality to investigate those dynamic processes as described above.(2) Inspired from the traditional dark-field imaging technology, we developed anew optical imaging system named dual-wavelength dark field microscopy (DWD) forthe selective detection of plasmon nanoparticles in noisy surroundings. By replacingthe regular light source with two different wavelength lasers (one at the resonancefrequency, the other one is shifted away from that wavelength), gold nanoparticles canbe readily distinguished in complex environment by two wavelength differenceimaging.(chapter2). Besides, with this method, we further studied the interactionsbetween gold nanoparticles and cancer cells by DWD method. We analyzed the diffusion mode of gold nanoparticles on live cell membrane and explained the dynamiccellular uptake process (chapter3). Moreover, we also investigated the localizationand orientation of single gold nanorod in3D by dual-wavelength dark-field microscopy.Gold nanorods split their surface plasmon resonance into transverse and longitudinalmodes due to theirs inherent morphological anisotropy. By capturing the dynamicmovement of single gold nanorod in solution, we elucidated the translationallocalization information and rotational dynamics in3D (chapter4). Then, thediffusion dynamics of protein functionalized gold nanorods were studied on livingHela cell membrane with this imaging mode. We found that the conjugation processbetween gold nanorod and receptor on living cellular surface was independent anduncorrelated with their lateral diffusion mode (chapter5).(3) Cell penetrating peptides have been extensively applied as efficientintracellular delivery platform for drug and gene delivery. By using lipid bilayer as asimplified model, we can deduce basic interaction mechanisms occurred on living cellsystem. In this work, we discussed the motion of gold nanoparticles coupled with acommon cell penetrating peptide (Tat) on neutral lipid bilayer by total internalreflection technology. We found that the adsorption process of Tat functionalized goldnanoparticles on lipid bilayer was very slow. The diffusion motion of these particleswas confined once the adsorption occurs. Based on dynamic information, we foundthat the gold nanoparticles could form a small domain on lipid bilayer. This processwas further validated by the gold nanorod orientational information on lipid bilayer(chapter6).(4) Gold nanocluster has emerged as a robust fluorescent contrast agent recently.They exhibit many advantages like facile fabrication process, low cellular toxicity,highly quantum yield and so on. In this part, we fabricated gold nanoclusters under agentle condition. These nanoclusters were able to target tumor cells by conjugatingwith folic acid. With a regular fluorescent microscope, we successfully detectednanoclusters labeled tumor cells with high efficiency. In addition, we also developedanother kind of cluster with different color (i.e. silver nanoclusters) which alsoexhibited good targeting capability for tumor cells (chapter7).