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Surface-enhanced Raman scattering (SERS) from gold and silver nanoparticles suspended in solution enables a more quantitative level of analysis relative to SERS from aggregated nanoparticles and roughened metal substrates. This is due to the more predictable and consistent near field enhancement regions created by isolated nanoparticles, and to averaging over the many nanoparticles that diffuse through the excitation beam during the measurement. However, we find that localized heating of the solution by the focused excitation leads to thermophoresis which alters the nanorod concentration in the focal volume and therefore impacts quantitative analysis. Since many phenomena may impact the Raman signal, we record both the Rayleigh and Raman scattering from gold nanoparticle solutions. This allows us to distinguish molecular processes from depletion of nanoparticles in the excitation beam. We observe that the concentration of nanorods can deplete to less than 50% of its original value over 100 second timescale, which are consistent with a thermophoretic effect driving nanoparticles from the beam spot. We also find that the particle motion drives convection within the sample cell that further contributes to signal instabilities.
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This content will become publicly available on December 1, 2025
Surface‐Enhanced Raman Scattering Sensors Employing a Nanoparticle‐On‐Liquid‐Mirror (NPoLM) Architecture
Abstract Surface‐enhanced Raman scattering (SERS) sensors typically employ nanophotonic structures that support high‐field confinement and enhancement in hotspots to increase the Raman scattering from target molecules by orders of magnitude. In general, high field and SERS enhancement can be achieved by reducing the critical dimensions and mode volumes of the hotspots to nanoscale. To this end, a multitude of SERS sensors employing photonic structures with nanometric hotspots have been demonstrated. However, delivering analyte molecules into nanometric hotspots is challenging, and the trade‐off between field confinement/enhancement and analyte delivery efficiency is a critical limiting factor for the performance of many nanophotonic SERS sensors. Here, a new type of SERS sensor employing solid‐metal nanoparticles and bulk liquid metal is demonstrated to form nanophotonic resonators with a nanoparticle‐on‐liquid‐mirror (NPoLM) architecture, which effectively resolves this trade‐off. In particular, this unconventional sensor architecture allows for the convenient formation of nanometric hotspots by introducing liquid metal after analyte molecules are efficiently delivered to the surface of gold nanoparticles. In addition, a cost‐effective and reliable process is developed to produce gold nanoparticles on a substrate suitable for forming NPoLM structures. These NPoLM structures achieve two orders of magnitude higher SERS signals than the gold nanoparticles alone.
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- Award ID(s):
- 1847203
- PAR ID:
- 10611479
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Small Methods
- Volume:
- 8
- Issue:
- 12
- ISSN:
- 2366-9608
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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