Synthesis And Properties Of Surface-Controlled Metal Oxides Micro/Nanocrystals, Application Of Nanocrystals In Biomolecular Detection

Anisotropy is a basic property of single crystals,and the various facets ordirections in a crystal may exhibit different physical and chemical properties.Thus,surface architecture-controlled nanostructures are desirable for many applications.Forthis purpose,the controllable preparation of micro/nanocrystals with different shapesand exposed surfaces is very important and challenging.In this dissertation,using a mixture of fatty acid(such as oleic acid(OA))andorganic amine(such as ethylenediamine)as the solvent,which can be thought as onekind of ionic liquid(R-COOH + R-NH₂(?)R-COO^-+ R-NH₃⁺)as the growthenvironment,we designed a general route for the controllable preparation ofnanocrystals with different shapes and exposed surfaces.The key strategy is to varythe surface energy of the polar surfaces by strong electrostatic interactions betweenthe ions of the ionic liquid and the polar surfaces.With this concept,we successfullyachieved the controlling of exposed surfaces and morphologies of a wide range ofmetal oxide nanomaterials:(1)Using the mixture of fatty acid(such as oleic acid(OA))and organic amine(such as ethylenediamine)as the solvent,we have demonstrated a thermaldecomposition synthesis of ZnO hexagonal micro-pyramids,whosesurfaces are enclosed by polarized(000-1)and {101-1} planes.The newmorphology of ZnO hexagonal micro-pyramids not only enriches the ZnOnano-family,the abnormal {10-11 } facets may also provide new opticalproperties and applications.(2)We studied green emission of ZnO micro-pyramids by directly investigatingthe luminescence from the different crystal surfaces of ZnOmicrocrystallites by means of room temperature cathodoluminescence(CL).The relative strength of the green emission was found to be stronglydependent on the crystal surfaces.By discussing the atom structures of different crystal surfaces,it is concluded that the green emission mostlycomes from the defects on/near the surfaces.(3)We further extend this method to the morphology-controlled synthesis ofdiluted magnetic semiconductors and achieved Zn_1-xCo_xO and Zn_1-xMn_xO hexagonal micro-pyramids,whose surfaces are enclosed bypolarized(000-1)and {101-1} planes.The magnetic characterizationshows they are antiferromagnetic at high temperature but ferromagnetic atlow temperature.(4)Moreover,we successfully synthesized surface-controlled rock-type metaloxide nanocrystals with the same stratege:CoO and MnO octahedralnanocrystal with all exposed surfaces being polar {111} planes.It is notedthat the MnO octahedral nanocrystal assembled to three-dimensionalsuper-lattice structure.We also discussed the formation mechanism.At last,we studied the biomedical application of nanomaterials.Specifically,wehave developed a class of surface-enhanced Raman molecular beacons(SERSbeacons)with novel mechanisms for molecular recognition and signal amplification.The key strategy is based on the long-range plasmonic coupling and bioconjugatedgold nanoparticles.The long-range nature of plasmonic interactions should allow thedevelopment of SERS beacons to detect proteins,clustered receptors on cellmembranes,and intact viruses,based on the coupling of adjacent metallic NPs in ano-wash/single-step format.In comparison with fluorescence emission,SERS spectracontain narrow molecular signatures that are well suited for multiplexing andbackground subtraction.