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Fiber sensors for molecular detection using Raman and surface enhanced Raman scattering

Abstract

In this dissertation, highly sensitive optical fiber sensors based on Raman spectroscopy (RS) and surface-enhanced Raman scattering (SERS) are studied with focus on applications in various chemical and biological detections. In particular, two main categories of optical fibers have been used as the sensing platforms: one is the conventional multimode optical fiber and the other is the hollow core photonic crystal fiber (HCPCF). For the conventional multimode optical fiber, we've developed two types of probes using SERS techniques: the first is based on a double substrate "sandwich" structure with colloidal metal nanoparticles, and the second is based on interference lithography-defined nanopillar array structure on the fiber facet with the metal film deposition. For the HCPCF, the photonic bandgap guiding mechanism provides an ideal sensing platform because the confinement of both light and sample inside the fiber enables direct interaction between the propagating wave and the analyte. We demonstrate that by filling up the air channel(s) of the fiber with gas or liquid samples, it can significantly increase the sensitivity of the sensors in either regular Raman or SERS applications. For RS applications, these fiber sensors were tested with ambient gases, organic vapors, and biomedically important glucose molecule. For SERS application, these fiber sensors were evaluated with Rhodamine 6G, trans-1,2-bis(4-pyridyl)-ethylene, toluene vapor, 2,4-dinitrotoluene vapor, proteins and bacteria. We also demonstrate that these fiber sensors can be integrated with the portable Raman spectrometer in order to make it practical for out-of-laboratory applications. The techniques developed in this study are expected to have significant impact in chemical, biological, environmental, national security, and other applications.

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