Advances in Raman and Surface-Enhanced Raman Spectroscopy: Instrumentation, Plasmonic Engineering and Biomolecular Sensing




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Raman spectroscopy is a powerful technique for label-free molecular sensing and imaging in various fields. High molecular specificity, non-invasive sampling approach and the need for little or no sample preparation make Raman spectroscopy uniquely advantageous compared to other analytical techniques. However, Raman spectroscopy suffers from the intrinsic limitation of weak signal intensity. Therefore, time-sensitive studies such as diagnosis and clinical applications require improving the throughput of Raman instrumentation. Alternatively, surface-enhanced Raman scattering (SERS) improves the sensitivity by 10^6 to 10^14 times, making the weak Raman intensity no longer a limitation. Nevertheless, it is still a big challenge to engineer plasmonic substrates with high SERS enhancement, good uniformity and reproducibility. This thesis presents advances in: (1) Raman instrumentation towards high-throughput, environmental, biological and biomedical analysis; (2) SERS substrates with high enhancement factor (EF), uniformity and reproducibility; (3) biosensing applications including imaging of cell population and detection of biomolecules towards high time efficiency and sensitivity. In Raman instrumentation, we have built a high-throughput line-scan Raman microscope system and a novel parallel Raman microscope based on multiple-point active-illumination and wide-field hyperspectral data collection. Using the line-scan Raman microscope, we have performed chemical imaging of intact biological cells at the cell population level. We have also demonstrated more flexibility and throughput from the active-illumination Raman microscope in rapid chemical identification and screening of micro and nanoparticles and bacterial spores. Both Raman microscopes have been used to evaluate the large-area SERS uniformity of DC-sputtered gold nanoislands, a low-cost means to fabricate plasmonic substrates. In plasmonic engineering, we have introduced patterned nanoporous gold nanoparticles that feature 3-dimensional mesoporous network with pore size on the order of 10 nm throughput the sub-wavelength nanoparticles. We showed that the plasmonic resonance can be tuned by geometrical engineering of either the external nanoparticle size and shape or the nanoporous network. As an example, we have developed disk-shaped entities, also known as nanoporous gold disks (NPGD) with highly uniform and reproducible SERS EF exceeding 10^8. Label-free, multiplexed molecular sensing and imaging has been demonstrated on NPGD substrates. Using the line-scan Raman microscope and the NPGD substrates, we have successfully developed a label-free DNA hybridization sensor at the single-molecule level in microfluidics. We have observed discrete, individual DNA hybridization events by in situ monitoring the hybridization process using SERS. The advances and promising results presented in this thesis demonstrate potential impact in Raman/SERS imaging and sensing in environmental, biological and biomedical applications.



Raman spectroscopy, Biomolecular sensing


Portions of this document appear in: Qi, Ji, and Wei-Chuan Shih. "Performance of line-scan Raman microscopy for high-throughput chemical imaging of cell population." Applied Optics 53, no. 13 (2014): 2881-2885. And in: Zeng, Jianbo, Ji Qi, Fuquan Bai, Jorn Chi Chung Yu, and Wei-Chuan Shih. "Analysis of ethyl and methyl centralite vibrational spectra for mapping organic gunshot residues." Analyst 139, no. 17 (2014): 4270-4278. And in: Qi, Ji, and Wei-Chuan Shih. "Parallel Raman microspectroscopy using programmable multipoint illumination." Optics Letters 37, no. 8 (2012): 1289-1291. And in: Qi, Ji, Jingting Li, and Wei-Chuan Shih. "High-speed hyperspectral Raman imaging for label-free compositional microanalysis." Biomedical optics express 4, no. 11 (2013): 2376-2382. And in: Liu, Chih-Hao, Ji Qi, Jing Lu, Shang Wang, Chen Wu, Wei-Chuan Shih, and Kirill V. Larin. "Improvement of tissue analysis and classification using optical coherence tomography combined with Raman spectroscopy." In Dynamics and Fluctuations in Biomedical Photonics XI, vol. 8942, p. 894208. International Society for Optics and Photonics, 2014. And in: Sudheendran, Narendran, Ji Qi, Eric D. Young, Alexander J. Lazar, Dina C. Lev, Raphael E. Pollock, Kirill V. Larin, and Wei-Chuan Shih. "Line-scan Raman microscopy complements optical coherence tomography for tumor boundary detection." Laser Physics Letters 11, no. 10 (2014): 105602. 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, 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: Li, Ming, Jing Lu, Ji Qi, Fusheng Zhao, Jianbo Zeng, Jorn Chi-Chung Yu, and Wei-Chuan Shih. "Stamping surface-enhanced Raman spectroscopy for label-free, multiplexed, molecular sensing and imaging." Journal of biomedical optics 19, no. 5 (2014): 050501. And in: Qi, Ji, Jianbo Zeng, Fusheng Zhao, Steven Hsesheng Lin, Balakrishnan Raja, Ulrich Strych, Richard C. Willson, and Wei-Chuan Shih. "Label-free, in situ SERS monitoring of individual DNA hybridization in microfluidics." Nanoscale 6, no. 15 (2014): 8521-8526.