The Preparation And Optical Properties Of ZnO:Eu³⁺ Nanocrystals, ZnO/Au Nanocomposites And Ultrasensive DNA Detection

In this thesis, ZnO nanomaterials were chosen as the subject of investigation, which was focused on the synthesis and optical properties of Eu3+-doped ZnO nanocrystals by a hydrothermal process, the synthesis and characterization of water-soluble ZnO/Au nanocomposites investigated to apply the ZnO/Au nanocomposites in ultrasensitive DNA detection. The details are as follows:(1) Trivalent europium ions doped zinc oxide nanocrystals were prepared by a hydrothermal process. The XRD patterns indicate that Eu3+ ions are successfully doped into the crystal lattice of ZnO matrix with inversion antisymmetry. The ZnO: Eu3+ nanocrystals exhibit a sharp red luminescence emission under the wavelength of 488 nm excitation, which is from the intra-4f transitions of Eu3+ ions. The 5D0-7F2 emission comes from an allowed electric-dipole transition and its intensity is the strongest. The PL peaks of Eu3+ ions can be observed even under the nonresonant excitation of 325 nm. It is explained by an energy transfer mechanism in which the energy is transferred from the defect state of ZnO matrix to Eu3+ ions in ZnO: Eu3+ nanocrystals.(2) The water-soluble and stable ZnO/Au nanocomposites were synthesized by the growth of Au on the surface of ZnO nanocyrstals. The sturcutre of the nanocomposites was characterized by the high-resolution TEM and XRD. The results indicated that ZnO/Au nanocomposites are heterostructures.(3) The water-soluble ZnO/Au nanocomposites were successful prepared with the aid of sonication. The size distribution and morphology of the ZnO/Au nanocomposites were characterized by the TEM and SAED. The UV-vis absorption spectra of ZnO/Au nanocomposites exhibited well-defined exciton band of ZnO QDs in the ultraviolet region(250-400 nm). The plasmon absorption band of Au nanocrystals was observed in the visible region (400-700 nm). With increasing the amount of Au on the surface of ZnO, the characteristic gold plasmon absorption bands in ZnO/Au composites had a red-shift, due to the electron transfer from Au to ZnO QDs. The photoluminescence of ZnO/Au nanocomposites was observed. Moreover, the enhancement of resonance Raman scattering of the ZnO/Au nanocomposites was observed with excitation of 325 nm light from He-Cd laser.(4) A novel method for identifying DNA microarrays based on ZnO/Au nanocomposites functionalized with thiol-oligonucleotide as probes is descried here. DNA labeled with ZnO/Au nanocomposites has a strong Raman signal even without silver acting as a surface enhanced Raman scattering promoter. The resonance multiple-phonon Raman signal of the ZnO/Au nanocomposites as a spectroscopic fingerprint is used to detect a target sequence of oligonucleotide. This method exhibits extraordinary sensitivity and the detection limit is at least 1 femtomolar.