Plasmonics Nanosensors for Improving the Sensitivity of Surface Enhanced Raman Spectroscopy

dc.contributor.advisorWolfe, John C.
dc.contributor.advisorShih, Wei-Chuan
dc.contributor.committeeMemberWood, Lowell T.
dc.contributor.committeeMemberBao, Jiming
dc.contributor.committeeMemberYu, Cunjiang
dc.creatorMotwani, Pratik Inder
dc.creator.orcid0000-0001-9810-4948 2015 2015
dc.description.abstractOver the past four decades, the development of advanced techniques for fabricating metallic nanostructures has reinvigorated interest in using surface-enhanced Raman spectroscopy (SERS) for practical applications in molecular sensing and chemical compositional analysis. Although numerous SERS substrates have been reported, most lack the reproducibility, structural uniformity, high density of strong field regions-hot spots, large active area, and low cost required for applications. In this work, SERS substrates that address these issues are developed and characterized. One of the earliest and simplest SERS substrate was evaporated Au/Ag nano-islands on glass substrates. However, the adhesion of these nano-islands is poor, particularly in aqueous environments. We showed that the use of sputter-deposition, instead of evaporation, provides reliable adhesion and, additionally, a practical way to control nucleation and film growth. By optimizing process conditions, we were able to induce nano-gaps in the films, which are known to be associated with a strong SERS response. In this work, through correlation between the process conditions, film morphology and SERS response, we have been able to obtain enhancement factors (EF) of 5 million, 5 times higher than the best evaporated films. More recently, nanoporous gold (NPG), a bicontinuous 3-D porous gold structure formed by free corrosion of Au/Ag alloys, has generated considerable interest as a SERS substrate. NPG features a high density of hot spots and a tunable plasmon resonance. The structural evolution of NPG/Au bilayer films and its effects on SERS intensity were studied in detail. By optimizing pore structure, we were able to increase EF by a factor of 6 over the state-of-the-art; a 75-fold increase was achieved by optimizing the gold-layer thickness. Patterning the NPG film into sub-wavelength disk shaped structures (NPGDs) produces EFs as high as 500 million. Finally, NPG and patterned gold sensors were formed on optical fiber substrates to explore plasmonics on optical fibers for remote sensing applications. In the first approach, NPG was deposited on fibers with cylindrical and tapered ends. In the second, periodic arrays of gold sensors were fabricated using ion beam proximity lithography, a high throughput approach where many fibers can be patterned simultaneously.
dc.description.departmentElectrical and Computer Engineering, Department of
dc.format.digitalOriginborn digital
dc.identifier.citationPortions of this document appear in: Qi, Ji, Pratik Motwani, Mufaddal Gheewala, Christopher Brennan, John C. Wolfe, and Wei-Chuan Shih. "Surface-enhanced Raman spectroscopy with monolithic nanoporous gold disk substrates." Nanoscale 5, no. 10 (2013): 4105-4109. And in: Qi, Ji, Pratik Motwani, Jianbo Zeng, John C. Wolfe, and Wei-Chuan Shih. "Morphological, plasmonic and SERS characterization of DC-sputtered gold nanoislands." Biomedical Spectroscopy and Imaging 4, no. 1 (2015): 95-103. And in: Qi, Ji, Pratik Motwani, John C. Wolfe, and Wei-Chuan Shih. "High-throughput Raman and surface-enhanced Raman microscopy." In Biomedical Vibrational Spectroscopy V: Advances in Research and Industry, vol. 8219, p. 821903. International Society for Optics and Photonics, 2012.
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectRaman spectroscopy
dc.titlePlasmonics Nanosensors for Improving the Sensitivity of Surface Enhanced Raman Spectroscopy
dc.type.genreThesis College of Engineering and Computer Engineering, Department of Engineering of Houston of Philosophy


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