Tandem Optical Detection Strategies Based on Surface Enhanced Raman Scattering (SERS) Spectroscopy

Surface enhanced Raman scattering (SERS) spectroscopy is a widely used analytical tool. Not only does SERS show promise for detecting small amounts of analytes, but combining SERS with other advanced analytical methods may add insight into nanoscale static and dynamic phenomena.

In this thesis, the history and advantages of SERS are first addressed in Chapter 1, followed by introducing two different approaches to develop new measurement methodologies based on SERS in following chapters. First, surface plasmon resonance (SPR) spectroscopy is correlated with SERS in the Kretschmann configuration, as demonstrated by successfully recording SPR sensorgram and SERS spectra separately and simultaneously, which is introduced in Chapter 2. In addition to a critical test to demonstrate its typical SPR function, Raman scattering from STV-AuNPs/biotinylated gold thin film was enhanced by a combination of surface plasmon from AuNPs and thin Au film. Also, the SERS spectra were simultaneously detected with SPR sensorgram, providing chemical insight into binding events, which were not detectable by SPR alone. By analyzing the spectra with multivariate curve resolution analysis, SPR-SERS spectroscopy demonstrated its potential to distinguish specific binding signals from the net sensorgram, thereby expanding the capabilities of SPR spectroscopy.

Chapter 3 introduces SERS in tandem with amperometry exploited to monitor the behavior of single Ag nanoparticles (AgNPs) functionalized with Raman reporter, 1,4-bis(2-methylstyryl)benzene (bis-MSB), when they are transported to single nanopores. To that end, highly ordered nanopore electrodes arrays (NEAs) with a single Au ring electrode were used to electrostatically capture bis-MSB AgNPs, characterized by simultaneous amperometry and SERS spectroscopy of AgNP oxidation and enhanced Raman scattering by bis-MSB at silver-gold hot spots, respectively. The frequency and magnitude of oxidation spikes increased with stepwise increases in DC voltage, and characteristic bis-MSB SERS spectra were observed. Under AC excitation, on the other hand, two distinctly different types of SERS signals were observed, independent of frequency and amplitude- strong, transient spectra and slow monotonically diminishing spectra. We hypothesize that the former behavior results from AgNP aggregates, while the latter occurs due to multiple incomplete AgNP oxidation events in succession. These results show that attoliter-volume NEAs are competent to acquire concurrent SERS spectra and amperometry of single nanoparticles and that together these measurements can illuminate the collision dynamics of the nanoparticles in confined environments. Overall, this work illustrates how combining SERS with other analytical tools yields measurements with improved sensitivity and characterization potential. The possibility of combining with surface plasmon polariton measurements and nanopore amperometry produces a versatile technique which should be applicable to many fields.