Investigation of SERS Frequency Fluctuations Relevant to Sensing and Catalysis

Abstract

The excitation of plasmon resonances on nanoparticles generates locally enhanced electric fields commonly used for sensing applications, and energetic charge carriers can drive chemical transformations as photocatalysts. The surface-enhanced Raman scattering (SERS) spectra from mercaptobenzoic acid (MBA) adsorbed to gold nanoparticles (AuNP) and silica-encapsulated gold nanoparticles (AuNP@silica) can be used to assess the impact of energetic charge carriers on the observed signal. Measurements were recorded using a traditional point-focused Raman spectroscopy and a wide-field spectral imaging approach to assess changes in the spectra of the different particles at increasing power density. The wide-field approach provides an increase in sampling statistics and shows evidence of SERS frequency fluctuations from MBA at low power densities, where it is commonly difficult to record spectra from a point-focused spot. The increased spectral resolution of the point spectroscopy measurement provides improved peak identification and the ability to correlate the frequency fluctuations to charged intermediate species. Interestingly, our work suggests that isolated nanoparticles may undergo frequency fluctuations more readily than aggregates.

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“…For SERS measurements, 1 mL of synthesized AuNPs were centrifuged for 25 min at 6000 rpm, and the supernatant was decanted from the pellet, to remove excess citrate [39]. The pelleted particles were resuspended in 1 mL of a 1:1 mixture of acetonitrile and water.…”

Multipolar Raman Scattering vs Interfacial Nanochemistry: Case of 4-Mercaptopyridine on Gold

“…Yet, multipolar Raman scattering continues to be under-appreciated, even in the context of tracking chemical transformations using plasmon-enhanced Raman scattering . This is surprising, given the prevalence of spectral fluctuations in high spatial resolution/ultrasensitive TER measurements, particularly under ambient conditions. ,, In this work, we stress the importance of considering multipolar Raman scattering to understand the brightest TER spectra of 4-MPY on gold.…”

“…11 This is surprising, given the prevalence of spectral fluctuations in high spatial resolution/ultrasensitive TER measurements, particularly under ambient conditions. 4,9,13 In this work, we stress the importance of considering multipolar Raman scattering to understand the brightest TER spectra of 4-MPY on gold.…”

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“…This method has successfully been used to investigate and localize short-lived species resulting from molecular reactions to the tips of gold nanostars, where the field confinement is expected to be most intense. 35,43 In the present study, we report novel P-GERTs with bipyramid cores and compare their SERS localizations, spectra, and intensities relative to the incident polarization to traditional bipyramid aggregates to elucidate how energy couples within the nanogaps at the structures. To do this, we employ spectral SERS imaging, which enables direct correlation of changes in the SERS emission and localization with respect to polarization in both the spatial and spectral domains.…”