Nanogap embedded TiO2 photonic crystals for enhanced fluorescence and surface dielctrophoreis of DNA
Abstract
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] One of the most commonly used detection tool in clinical diagnostics, life science research, chemical, and biological sensors is fluorescence. Because of its cost effective, sensitive, and specific nature fluorescence has emerged as one of the key techniques used for detection of analytes in many biological applications like cell imaging, DNA amplification, and sequencing etc. However, there has been a growing need to detect weak signals and improve the contrast levels in fluorescence images, this is essential for detecting single fluorophores and reducing the limit of detection for fluorescence based biosensing. In recent years, researchers have developed many methods like total internal reflection microscopy (TIRF), confocal microscopy, and two-photon excitation microscopy (TPEM), which improves the fluorescence emission, thereby increasing the detection sensitivity. To further enhance the output of this technique, a number of nano-patterned structures like photonic crystals, plasmonic gratings, and metallic bowtie nano-antenna's have been developed. These nano-structures basically enhance the electric field intensity which can be used to couple light to the surface-bound fluorescent dye molecules thereby providing extreme signal amplification necessary for detecting low quantities of biomolecules tagged with fluorophores. Photonic crystals are an optical media with periodic modulation of the optical properties like refractive index. The optical resonances seen in photonic crystal surfaces are called as guided mode resonances. When these nano-structured surfaces or gratings are illuminated, only the 0th reflected and transmitted diffraction orders can propagate, and higher diffraction orders can couple to leaky modes in the photonic crystals under certain resonant conditions. In this thesis, we present a cheap and simple fabrication technique for producing polymethylsilsesquioxane (PMSSQ) based gratings embedded with nano-gaps using micro-contact printing where a commercially available high-definition (HD) DVD-Rs is used as the mold to obtain the starting PDMS stamps. The nano-gaps are formed spontaneously within the grating structure as a result of tensile strain in the elastomeric PDMS stamp during the printing process. This method overcomes all the shortcomings of conventional lithography, e-beam lithography and reactive ion-etching (RIE) procedures, as the nano-structured substrates can be fabricated comparatively fast, easily and in a low production cost. These nano-gap embedded PMSSQ gratings can then be used as a base pattern for depositing dielectric layers to form photonic crystals or metal layers for plasmonic nanostructures. Using this approach we have fabricated nano-gap embedded TiO2 photonic crystals for enhanced fluorescence emission. These nano-structured substrates because of their enhancement will have many applications, in bio-sensing area as it can lower the detection limit of analytes, single molecule imaging, and other diffraction-limited optics
Degree
M.S.
Thesis Department
Rights
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