Surface plasmon resonance (SPR) active nanohole array substrates offer a diverse biosensing platform with high sensitivity and unique characteristics. This dissertation investigates the sensitivity and fundamental SP features of various nanohole array substrates and demonstrates higher sensitivity than conventional continuous gold platforms, tunability to specific analytes, and great enhancement of the local field intensity. Novel instrumentation and analytical techniques are developed and utilized to assess the nanohole array SPR sensing substrates in the near infrared as well as with interaction of other nanostructures.
The nanohole array substrates are evaluated throughout the near-infrared (NIR) region by novel SPR instrumentation and methodology that extends the working SPR wavelength range and measurement reliability. Development of a robust NIR-SPR instrument allows access to higher wavelength ranges where sensitivity is improved and novel SP modes and plasmonic materials may be investigated. Different aspects of the NIR-SPR instrument, including temporal stability, mechanical resilience and sensitivity, are evaluated and presented. Furthermore, a method is developed for improving precision and accuracy of empirically determined SP penetration depth, a merit of SPR spectroscopy sensitivity. The technique incorporates an adsorbate-metal bonding effect which improves the consistency in the penetration depth value calculated at different adsorbate thicknesses from 41-1089% relative deviation (without bonding effect) to 2-11% relative deviation (with bonding effect). It also improves the experimental agreement with theory, increases the accuracy of assessing novel plasmonic materials and nanostructures, and increases the precision in adsorbate parameters calculated from the penetration depth value, such as thickness, binding affinity, and surface coverage.
Utilizing this NIR-SPR instrument and improved technique for calculation of penetration depth, the sensitivity and various SP modes of the nanohole arrays throughout the NIR range are evaluated, and an improvement in sensitivity compared to conventional continuous gold is observed. Both the Bragg SPs arising from diffraction by the periodic holes and the traditional propagating SPs are characterized with emphasis on sensing capability of the propagating SPs. There are numerous studies on the transmission spectroscopy of nanohole arrays; however this dissertation presents one of the few studies in Kretschmann mode, and the first in the near infrared, where greater surface sensitivity is observed. The sensitivity profile of various nanohole array parameters (periodicity, diameter, excitation wavelength) and SP modes is also presented.
Further control and enhancement of the SP field is pursued by interaction between nanohole array substrate and nanoparticles to exploit field intensification between plasmonic structures, i.e. gap mode enhancement. Under specific conditions, the SPs couple together and the electric field between the structures is amplified and localized, which may be exploited for sensing purposes and surface enhanced techniques, including tip enhanced Raman spectroscopy (TERS) or surface enhanced Raman spectroscopy (SERS). A technique for observing nanohole array-nanoparticle distance dependent SP interaction is developed and utilized to demonstrate SP interaction. Scanning probe microscopy controls the position of a single nanoparticle (SNP) affixed to an atomic force microscope probe, and the location specific interaction of the SNP-nanohole array surface plasmons is measured by darkfield surface plasmon resonance spectroscopy. Coupling of the nanoparticle to the nanohole array exhibits a maximum when the SNP resides within a nanohole, which resulted in a maximum SPR wavelength shift of 17 nm and an increase in scatter intensity. This dissertation presents the first empirical observations of SPM controlled gap mode enhancement of more complex nanostructures and allows for optimization of positioning prior to use in sensing.
|Advisor:||Booksh, Karl S.|
|Commitee:||Chui, Siu-Tat, Johnston, Murray, Rozovsky, Sharon|
|School:||University of Delaware|
|Department:||Department of Chemistry and Biochemistry|
|School Location:||United States -- Delaware|
|Source:||DAI-B 76/09(E), Dissertation Abstracts International|
|Keywords:||Nanostructure, Spectroscopy, Surface plasmon resonance|
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