DEVELOPMENT OF CUTTING-EDGE SERS AND TERS TECHNOLOGIES FOR ENVIRONMENTAL CHALLENGES

Date

2023-12-19

Author

Demirtaş, Özge

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There is a growing demand for rapid and non-destructive detection methods that provide reliable fingerprint information of trace-level environmental analytes. Surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) enable label-free chemical identification and quantification. Enhancement of both incident and scattered electromagnetic fields at the close vicinity of metal nanostructures in SERS and that of the tip in TERS is achieved through proper choice and design of the plasmonic nano-antennas. We present cutting-edge SERS substrate preparation methods highly promising in signal enhancement and reproducibility, with high benefit-cost ratio. We demonstrate monolayer close-packed assemblies of multispiked gold nanoparticles (NPs) capable of detecting 10 fM of the crystal violet (CV) and 1 μM level ammonium nitrate. We also report in-situ growth of surfactant-free Ag nanostructures and Au-Ag alloy NPs on filter paper using a one-step chemical reduction. With Ag nanostructures, the C-N symmetric stretching mode of urea nitrate is detectable down to 1 μM concentration, while Au-Ag alloy NPs enable the detection of multiplexed Rhodamine 6G, CV, and brilliant cresyl blue. We present a cutting-edge TERS design that facilitates epi-illumination and collection configuration, enabling characterization of both opaque and transparent samples while eliminating residual background signals associated with side illumination. Our design allows for the use of three different laser wavelengths, making it suitable for a wide range of spectral responses from both the atomic force microscopy tips and the analytes. Further enhancement of TERS signal can be achieved through plasmon nanofocusing, involving the propagation of surface plasmon polariton (SPP) through the tip’s end after exciting SPP on the metal tip shaft. We employ laser-induced periodic surface structuring with femtosecond pulses, enabling multiple tip modifications simultaneously.

Subject Keywords

Localized Surface Plasmon, Surface-enhanced Raman Spectroscopy, Tip-enhanced Raman Spectroscopy

URI

https://hdl.handle.net/11511/107855

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Graduate School of Natural and Applied Sciences, Thesis