Fe₃O₄ Orγ-Fe₂O₃@Au Core-shell Structured Nanoparticles: Synthesis, Characterization, And Application In HBV DNA Diagnosis

In this thesis, we describe the synthesis of water-soluble Fe3O4 orγ-Fe2O3@Au nanoparticles through a seed-mediated approach, by which gold shells were hetergeneuously grown onto surfaces of magnetic iron oxide nanoparticles. From TEM images, it is found that these composite nanoparticles are dispersed quite well from each other. Furthermore, the product particles can always be assigned into two categories, one is the particles with a diameter less than 10 nanometer; while the other of relatively larger sizes. Though TEM hardly shows the core-shell structure of these particles (due to the higher electronic density of gold as compared to iron oxde), energy dispersive spectroscopy (EDS) verifies the coexistence of Fe and Au in the concerned particles of either the larger or smaller sizes. This is also confirmed convincingly by results of high-gradient magnetic filtration (HGMF), which demonstrates the negligible amount of pure Au nanoparticles among particles of gold characteristic. Therefore, we conclude that the gold shell do form on surface of magnetic iron oxide nanoparticles, and the large-sized particles are largely of gold character, while the smaller ones of mainly iron composition. For small-sized particles with a relatively thinner gold shell, their selected area electron diffraction (SAED) pattern shares the similarity of face-centered cubic structure with the pattern of pure Au nanoparticles on the one hand, and differs somewhat from that of magnetic iron oxide particles on the other hand. Further comparison between these SAED patterns indicates that about 12% lattice compression had occurred on the relatively thinner gold shell, and the driving force for this, we suggest, is the coherency strain, which enables the shell material at the heterostructured interface to adapt the lattice parameters of the core, causing the Au atoms nearby the heterostructured interface pack more tightly than they usually do in pure Au nanoparticles. With the aid of HGMF, we also investigate influence of the synthetic conditions on the product Fe oxide core/Au shell nanoparticles. The seed concentration is found to play a key role on minimizing the fraction of pure Au nanoparticles, while that of citrate to Au3+ mole ratio affects mainly the mean thickness of gold shell of the product composite nanoparticles. To produce magnetic Fe oxide core/Au shell nanoparticles with a minimum fraction of pure Au particles and suitable thickness of gold shell, 0.7~1.0 ml as-synthesized suspension of the seeded superparamagnetic iron oxide nanoparticles (SPION) and a citrate to Au3+ mole ratio within the 38.85 to 124.16 range are suggested. Finally, we describe preparations of DNA probes labeled with pure Au and composite nanoparticles, as well as their applications in easy, cheap, and fast diagnosis of HBV DNA.