Theoretical and Experimental Characterization of Plasmonic Materials and Grating Based SPR Sensing
Chada, Ratna Reddy
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Plasmonics, the science and technology of the plasmons, is a rapidly growing field with substantial broader impact in numerous different fields, especially for bioapplications such as bio-sensing, biophotonics and photothermal therapy. Resonance effects associated with plasmonic behavior, i.e. surface plasmon resonance (SPR) and localize surface plasmon resonance (LSPR), are of particular interest because of their strong sensitivity to the local environment. SPR sensing techniques have made great strides in terms of instrumentation development and applications. SPR-based biosensing has gained prominence for label-free sensing using optical instruments. This thesis deals with the underlying physics of plasmon resonance, resonance effects in metallic nanostructures and their applications, characterization of plasmonic material properties using different theoretical models and grating-coupled SPR sensing. In Chapter 1, we discuss the physics of surface plasmon resonance and the excitation of surface plasmons in metal films using different coupling mechanisms such as prism, grating and waveguide coupling. A brief overview of different techniques for sensing SPR is given are discussed including wavelength, angle and intensity modulation. The fundamentals of LSPR in sub wavelength metallic nanoparticles are also discussed including its dependence on the size and shape of the particle as well as the dielectric properties of the background media. In Chapter 2, details of theoretical material characterization are presented that involve the use of Drude-Sommerfeld model and polynomial spline fits to obtain analytical expressions for experimental permittivity data. The extraction of the Drude-Sommerfeld model parameters from experimental absorption properties is demonstrated. In Chapter 3, we discus LSPR in metallic nanoparticles and its dependence on the size, and shape of the particle as well as the dielectric property of the background environment. Details of absorption spectra of gold nanorods and core-shell particles is presented. Computational modeling of the absorption spectrum of novel micelle-based magneto-plasmonic nanoplatforms is also presented along with their use in photothermal therapy. In Chapter 4, an experimental setup of a grating-coupled SPR biosensor is described. The calibration, characterization and modeling of this device is presented.