I. Plasmon-resonant cavity modes in 2D arrays of gold nanorods. II. Real-time detection of pathogens using Fourier-transform based image processing
Abstract
In the first chapter, hexagonal lattices of Au nanorods on a thin Au baseplate were shown to exhibit novel reflectance behavior with multiple resonant attenuations at visible and NIR wavelengths when irradiated at normal incidence. The number and spectral positions of these resonance modes can be varied by adjusting the nanorod height and the refractive index of the host medium. The experimental far-field reflectance spectra can be reproduced by utilizing 3D finite-element method (FEM) simulations, which also indicate these resonances to be associated with harmonic standing waves between nanorods. Quarter-wave modes are observed, with the nodes and antinodes located at the Au baseplate and nanorod tips, respectively. In addition to nanorod height and refractive index of the host medium, the number of harmonic resonances and their respective wavelengths increase with diameter-spacing ratio. Dispersion relations based on these standing-wave modes reveal strong retardation effects, correlated with the strength of transverse coupling between rods. Removal of the Au baseplate was predicted to result in resonant transmission through the nanorod arrays, at frequencies defined by half-wave cavity modes after simulation matching. This was confirmed upon the successful removal of the baseplate studies for both Au nanorods and also for Ag nanorods. Focused ion-beaming etching was employed to shave the tips of the Ag nanorods, due to their non-uniform growth. In the second chapter, a label-free pathogen detection platform was developed for rapid and sensitive biosensing, with real-time monitoring which is of great interest for counter-bioterrorism, and for the surveillance of infectious diseases. The detection platform is based on "immutable" capture ligands printed or stamped in a periodic pattern, which is optically imaged under darkfield conditions and subjected to fast Fourier transform analysis for pattern recognition, indicating capture of pathogens. Simulations guided the development of capture patterns for detecting the binding of multiple pathogens simultaneously within the same region of interest. It was shown that the fill factor needed for FFT-based detection is low (6%), but the size of the pattern imaged area affects the quality of the Fourier signal. The successful multiplex detection of multiple pathogens was achieved and can be further expanded, using appropriately selective ligand-pathogen combinations. The detection platform can fit onto a standard bench with opportunities for further miniaturization.
Degree
Ph.D.
Advisors
Wei, Purdue University.
Subject Area
Biochemistry|Materials science
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