Abstract:
Raman spectroscopy is a valuable technique for analyzing materials and their
properties. However, due to the small scattering cross-section of many analytes, only
weak signals with low signal-to-noise ratios (SNRs) are obtained. Researchers have
explored various methodologies to overcome these limitations and enhance the power
of this technique. Plasmonics, particularly Surface-Enhanced Raman Spectroscopy
(SERS), has garnered global attention as a means to overcome weak Raman intensity.
However, SERS has limitations and constraints, such as complex sample preparation
and high costs, that must be overcome for broader applicability.
This dissertation demonstrates that gradient two-dimensional (2D) SERS substrates
with multiple resonances improve the analysis of numerous samples. Such
substrates enable fast screening of various molecules. With conventional 2D substrates,
the signal from molecules is only enhanced when they are very close (a few
nanometers) to the substrate surface. To overcome this limitation, innovative, stable,
and three-dimensional (3D) SERS substrates based on spherical silica microspheres
(SMPs) are developed as carriers for metal nanoparticles (NPs). These novel substrates
offer the advantage of allowing analyses in all spatial directions, showing multiple
resonances, being cost-effectively synthesized, and being used in various solutions.
They address some of the limitations of conventional SERS substrates.
Furthermore, this doctoral thesis deals with advanced data analysis in SERS
and Raman spectroscopy, which can lead to difficulties interpreting the data. Advanced
data analysis is applied to identify subtle spectral differences and improve data interpretation.
However, optimizing and maintaining spectrometers' performance and calibration
stability over time is essential for reliable data interpretation. For this purpose,
a quality factor is introduced, which represents the fit between theoretically calculated
and experimentally measured spectral resolution (SR). This is applied to a commercial
spectrometer used in the dissertation.
In summary, this work addresses central challenges and weaknesses in Raman
spectroscopy, improving its applicability and addressing the associated challenges.
Surface-Enhanced Raman Spectroscopy (SERS)