Surface Structure Induced Fluorescence Characteristics Of3C-Sic And Au Nanoparticles And Its Application

With development of nanotechnology, more and more nanomaterials with novel structure and morphologies have been prepared. These nanostructures have wide range of applications in communications, military, environmental, energy, biomedical and some other fields. However, their applications are often affected by their surface and interfacial properties. Therefore, studies on surface and interfacial properties of nanostructures have always been a hot research subjects in nanomaterials science. In this dissertation, we select cubic silicon carbide (3C-SiC) and gold (Au) nanoparticles as representative nanomaterials. Fluorescence characteristics caused by the surface and interface structures are studied by TEM and fluorescence spectroscopy. We also use the fluorescence properties of the surface structure to detect biological signal. The obtained main results are described as follows:1. We prepare3C-SiC nanoparticles by chemical etching3C-SiC powder. By studying the PL spectra of3C-SiC nanoparticles in solutions with different pH values, we find that in addition to the emission from recombination of carriers caused by the quantum confinement effect, there is another emission with the wavelength at510nm and its intensity changes with pH value of solution. This arises from the structures induced by H+and OH-dissociated from water and attached to Si dimers on the modified Si-terminated portion of the nanoparticles. Different H+and OH-connections on the surface of nanoparticles in different pH values environment cause the intensity changes of its emission. According to this, the emission peaks are decomposed and the the ratio of intensities in510nm and440nm is shown to have a linear relationship with the pH values of solution in the range of5.6-7.4.2. Because nearly all intracellular processes function in a narrow pH range, intracellular pH (pHi) plays an important modulating role in many cellular events and the structural stability and functions of proteins are strongly affected by pHi. Traditional organic fluorescent probes for pHi detection have large toxic and unstable structures and cannot be traced when they get into cells. The newly developed nanoparticle-based nanosensing platforms for pHi detection have complex structures, large sizes and low measuring efficiency. According to the studies of last chapter, we describe a pH sensitive inorganic semiconductor fluorescent probe based on ultrathin3C-SiC nanoparticles which can effectively monitor pH in the range of5.6-7.4by taking advantage of the linear dependence between the fluorescent intensity ratio of the surface OH-and H+bonding states to band-to-band recombination and pH. And real-time intracellular pH (pHi) detection is demonstrated in living HeLa cells. The viability studies of HeLa cells that endocytose3C-SiC nanoparticles indicate that the3C-SiC nanoparticles have low cytotoxicity. The confocal microscopy and TEM studies show that3C-SiC nanoparticles distribute in the cytosol of cells, which mean that the pHi values detected by3C-SiC nanoparticles are the pH of cytosol.3. Because the singals detected by biological nanoprobes are always weak, a variety of ways to enhance the signal are needed in biological signal detection. It is well known that gold nanoparticles have surface plasmon resonance due to the electron excitation effect, and the distances between the surface of gold nanoparticles and dyes have a significant influence on the enhancement. So it is worth to study this effect clearly. Gold nanoparticles are prepared on asymmetric DNA double helical structures. By adjusting the length of the FAM terminated chain of dsDNA, the distance between the FAM and Au surface can be continuously adjusted and the corresponding relationship between the enhancement factors and distance is identified. TEM studies show the formed Au nanoparticles have some twinning structures and sharp corners. The distance between individual nanoparticles varies between2to4 nm and these nanoparticles form clusters with a size of～40nm. The mainly reason is that the outer part of DNA is the tri-phosphate group which contains negative charges, while the inner part is the base group and metallic NPs which mainly contain positive charges. This charge distribution affects the generation of gold nanoparticles and their agglomeration.