Study On Strong Confinement Structures In Micro-and Nano-Photonics And Their Applications In Biosensing And Bioimaging

This dissertation is mainly about the design and fabrication of the strong confinment elements in micro- and nano- photonics for sensing and imaging applications,especially in biomedical research.As typical strong confinement elements in the micro-scale photonics, planar optical waveguides are studied and designed in a way to be more compact in size and better suited for sensing applications.Metallic structures are proposed to be introduced so as to improve the sensitivity due to the strong enhancement from the surface plasmon resonance.On the othe hand,nano-scale photonics,where nanoparticles as the strong confinement elements play as a key role,have been attracting great attention during the last few years due to the extraordinary opportunities it offered in a variety of research fields.Two kinds of nanoparticles have been synthesized,characterized and engineered for biosensing,in vitro and in vivo bioimaging.In micro-scale strong confinement photonics structure studies,two types of waveguides are designed and analized using finite difference method.A minimized silicon dioxide optical waveguide with an etch-through antiresonant reflecting buffer and an air cladding is presented. The air cladding is used to achieve a high refractive index contrast thus to minimize the lateral size of the waveguide,while the antiresonant reflecting buffer is used to reduce the leakage loss due to the silicon substrate.According to the design,by introducing three periods of etch-through antiresonant reflecting strutures,a straight SiO₂ waveguide with a low leakage loss (＜0.01 dB/cm) and a bending radius as small as 15μm is obtained.The other waveguide structure is based on a commercially available polymer SU-8,which also has an air cladding.In order to redcue the leakage and bending losses,the SiO₂ buffer layer is etched partially.Systematic analysis on the waveguide including the single-mode condition,birefrigence and especially the bending behavior are performed.The numerical simulations indicate that the transition loss between the straight and bending sections dominants the bending loss and can be greatly reduced by introducing a lateral offset.Following the design,straight and bending waveguides are fabricated and characterized,which set basis for the future development in the integrated sensing applications. As for the strong confinement structures in nano-scale photonics,functionalized metallic and semiconductor nanoparticles have been synthesized,characterized and engineered for different biomedical applications.Gold and silver nanoparticles with different optical properties are obtained by manipulating their size,shape,composition and structure during the synthesis. The as-synthesized nanoparticles,such as silver nanospheres,gold nanorods and gold/silver core/shell nanorods are then functionalized with biomolecules for in vitro studies,including detecting,targeted labeling and multi-colored dark field imaing of human cancer cells,and gene delivery for drug addiction therapy.In vivo studies are also carried out with preliminary results showing that the gold nanorods are highly biocompatible to small animals even with an extremely high dosadge.The demonstration of several applications in biomedical research shows that these metallic nanoparticles are able to provide a powerful and promising nanosized platform for the diagnosis and therapy of desease.On the other hand,in vivo tumor targeting and imaging studies with functionalized semiconductor anisotropic nanocrystals are performed. Highly luminescent CdSe/CdS/ZnS quantum rods(QRs) are synthesized and encapsulated with PEGylated phospholipids,followed by conjugation with cyclic RGD peptides which specifically target the tumor vasculature.These functionalized QRs are then used for targeting and imaging the tumors in nude mice bearing pancreatic cancer xenografts(both subcutaneously and orthotopically planted).Detailed cytotoxicity studies are also performed with results indicating that the functionalized QRs have no observable toxic effect in the cellular and tissue levels, which reflects the vast potential of QRs as bright,photostable and biocompatible luminescent probes for the early diagnosis of cancer.These results greatly expanded the sensing and imaging aplicaitons of the nano-scale strong confinement structures in biomedical research.