Controllable Fabrication Of Nanomaterial Assembly And Its Applications In Cell Imaging

The investigations of nanoparticle assembly have promoted the development of nanocomposites in chemical and biological sensing, cell imaging and medical therapy. Combining the unique plasmon resonance properties of metal nanoparticles or fluorescence properties of semiconductor materials and biocompatibility of carbon nanomaterials, the nanocomposites demonstrate great potentials in biological imaging and cancer therapy. In this thesis, the dependence of surface plasmon resonance properties on particle morphology, size and plasmon coupling has been investigated, and then metal nanoparticle assembly as well as metal nanoparticle/carbon nanotube assembly have been facilely fabricated, which could be applied to the preparation of quantum dot/graphene nanocomposites. We have also investigated the potential applications of such nanocomposites in cell imaging and drug delivery. The main points are as follows:1. A general one-step route to synthesize Au crystals with various morphologies has been proposed. Starting from HAuCl4 in an aqueous medium and by employing tetracycline hydrochloride as the reducing agent and cetyltrimethylammonium bromide (CTAB) as the capping agent, it is very easy to get twinned tabular crystals, single crystalline nanoplates, and multi-twinned decahedra by modulating the molar ratio of CTAB with HAuCl4. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the three types of symmetric morphology. UV-vis-NIR. extinction spectra, dark field light scattering imaging and single particle spectra were used to investigate the dependence of surface plasmon resonance scattering on crystal size and morphology. The unique optical properties of the obtained crystals, including NIR absorption and dark field light scattering demonstrate their potential applications in cancer cell diagnostics and photothermal therapy. Moreover, a tentative explanation for the growth mechanism of Au crystals with different morphologies has been made.2. Linear chains of Au nanorods and bifurcated junctions of nanorods/nanospheres could be facilely fabricated via the cross-linking of H-type tetrakis(4-sulfonatophenyl)porphyrin (TPPS) aggregates in solutions. The tuning of the plasmon coupling between the Au nanocrystals has been demonstrated by varying the porphyrin concentration and thus the interparticle gap distances. The assembled nanocrystals were characterized by the extinction spectra and SEM images,ζ-potential measurements, dynamic light scattering analysis as well as resonance light scattering spectra confirmed the assembly was initiated in aqueous solutions other than solvent evaporation during the SEM specimen preparation. Further more, Finite-difference time-domain (FDTD) calculations showed that the redshift of the plasmon band exhibited a nearly exponential decay with increasing interparticle gap distances, giving rise to a "plasmon ruler equation". The gap distances determined according to this equation agreed well with the SEM observations. We also designed a biological procedure to investigate the interaction between Au nanocrystals and TPPS by the dark field light scattering technique, further confirming our view that TPPS preferentially bond to the end of Au nanorods to facilitate their end-to-end assembly.3. A novel strategy to prepare metal nanoparticle/carbon nanotube (CNT) hybrids through DNA linkage has been proposed. Both experimental and theoretical results demonstrated that the adsorption ability of single-strand DNA (ssDNA) on carbon nanotubes is correlative with electronic structure of natural bases. Based on the special interaction between ssDNA and CNTs, DNA modified Au nanoparticles could deposite on CNTs throughπ-πconjugate interaction, and the morphology, size, charge as well as the composition of metal nanoparticles could be rationally modulated according to experimental requirements. The conjugation chemistry did not perturb the unique intrinsic properties of each component, such as the unique plasmon properties of metal nanoparticles, and the affinity of CNTs for cancer cells. We have further investigated the interaction between nanocomposites and cancer cells using dark field light scattering imaging, and the results demonstrated that the internalization of nanocomposites into cancer cells depends on not only intrinsic affinity of CNTs but also biocompatibility of capped agents on decorated metal nanoparticles. Furthermore, the enhanced absorption of CNTs in the NIR region and the strong scattering of AgNSs in the visible region enable AgNS/CNT hybrids to be efficient agents for both cell imaging and cancer therapy.4. Quantum dots (QDs)/graphene hybrids have been facilely fabricated via DNA's cross-linking. It was found that QDs, which was first modified by DNA through colvalent bond, could be assembled on graphene surfaces throughπ-πstacking. The nanocomposites exhibited unique intrinsic properties of each component, such as high fluorescence intensity, good biocompatibility. By employing graphene as delivery vectors, we investigated the potential applications of the prepared nanocomposites in drug delivery, and it was found that the drug distribution could be visually observed by its own fluorescence. The internalization procedure of graphene could be monitored by QDs'fluorescence. In other words, the nanocomposites provided opportunities for monitoring both the drug delivery and vector distribution.In conclusion, the dependence of surface plasmon resonance properties of metal nanoparticles on morphology, composition and plasmon coupling has been investigated in this thesis. Based on the interaction between ssDNA and CNTs, we proposed a universal method for fabrication of metal nanoparticle/carbon nanotube assembly via DNA's cross-linking. The method could be further applied to prepare QDs/graphene assembly. The nanocomposites exhibited unique optical properties as well as good biocompatibility, which demonstrated great potentials in biological imaging and cancer therapy.