Development and characterization of plasmonic materials for chemical sensing: an investigation Into novel SPR architectures

Boyne, Devon A.
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University of Delaware
Surface plasmon resonance (SPR) spectroscopy is a rapidly growing field for chemical detection. Various SPR sensor architectures can offer high sensitivity, tunability and selectivity over a wide range of applications. Enhancements to this technique are obtained by introducing novel and modified designs capable of probing different optical regions. The contributing efforts of this dissertation aim to identify and characterize several of these platforms for use in real-world sensing applications. Herein, three basic types of SPR architectures are developed, conducting polymers as a replacement for conventional materials, a MIR-SPR sensor pad and composite-SPR sensors for selective applications. Conductive polymers represent an exciting addition to plasmonics as they offer new ways to apply SPR sensing for a reduced cost, in particular Polyaniline (PAni) has been identified in literature a possible candidate for SPR. In this dissertation several deposition methods for PAni are presented to obtain specific film parameters capable of supporting plasmonic behavior, including vacuum deposition and solution cast methods. Vacuum deposition methods exhibit good control over the thin film parameters, with roughness values (R RMS ) as low as 0.5 nm and a reduced amount of observable pin-holes. Additionally, the deposition methods described herein are applicable to the demonstration of polymer plasmonics as well the improvement of non-plasmonic applications of conducting polymers. Theoretical modelling reveals that certain films demonstrate sufficient sensitivity (~3770 nm/RIU) for SPR sensor applications. Experimental validation performed in this dissertation does not substantiate theoretical evidence, however identifies innate difficulties is the experimental demonstration and will be essential for subsequent investigations. In an attempt to expand SPR to different analytes and demonstrate a highly tunable sensor, a MIR-SPR sensing pad is developed with the capability of probing various regions within a single sample. The sensitivities and plasmonic characteristics are quantified over the MIR region with the highest sensitivities occurring between 2800 cm -1 and 2250 cm-1 (~15,200 +/- 2.2 nm/RIU). For specific MIR wavelength regimes, a 22 +/- 4% deviation is observed from theoretical values. Furthermore, discrepancies for determining the theoretical probing depth are identified and alleviated with a more robust method to verify experimental values with theoretical predictions. Finally, composite SPR materials are designed to promote further selectivity and tunability for SPR devices. Initially, a coupled waveguide plasmon resonance MIR-sensor is described that suggests high variability within the MIR regime and is successfully applied to quantitative and qualitative hydrocarbon detection in the ppb range. Moreover, a selective plasmon-plasmon sensor is optimized towards enhancement of sensitivity and modulation of signal by means of plasmon coupling. The optimization of a component parts reveals good tunability for future coupling experiments. Additionally, a deposition method for carbon nano-tubes (CNTs) is validated as a potential substrate for plasmonic coupling. Ultimately the studies described in this dissertation attempt to expand SPR spectroscopy to a wider array of analytes and increase the performance merits of SPR sensors.