Photonic sensor based on surface-enhanced raman scattering for the detection of trace chemicals

Abstract

The research presented in this thesis describes the development of a three-dimensional (3D) tapered optical fiber-based surface-enhanced Raman scattering (SERS) sensor for detecting trace chemicals. The developed system was capable of detecting rhodamine 6G (R6G) and crystal violet (CV) at Picomolar (pM) levels. A Scanning electron microscope (SEM) and an optical microscope were used to characterize the tapered fiber. The unique characteristics of the fabricated SERS substrate, such as the uniform distribution of analyte around a particular diameter of the fiber and a specific location where maximum SERS intensity was observed, have been presented. The developed sensor was used in the real-time detection of chemicals, allowing immediate adjustments. The detection limit of 10-7 M for R6G and 10-8 M for CV was achieved in real time. A seedless method was used to synthesize gold nanorods (GNRs) with localized surface plasmon resonance (LSPR) closer to the excitation wavelength. The prepared GNRs were tweezed successfully on the tapered fiber surface, and a minimum detectable limit of 10 pM was achieved for CV. A plasmonic structure using Zinc (Zn) and Zinc Oxide (ZnO) was developed using optical tweezing along the tapered fiber length. The effect of single and double tweezing was investigated. This plasmonic structure has potential applications in biosensing.