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Shape-Dependent Surface-Enhanced Raman Scattering under Modal Ultrastrong Coupling between Self-Assembled Gold
Zhiyu He1, Xu Shi2,3, Keiji Sasaki2
1Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
ACS Applied Materials & Interfaces
|December 11, 2025
Summary
Self-assembled gold nanoparticles on Fabry-Pérot cavities enhance surface-enhanced Raman scattering (SERS). Nanoparticle shape dictates SERS performance, with gold nanotriangles offering superior sensitivity in limited analyte conditions for advanced sensing applications.
Area of Science:
- Plasmonics
- Nanophotonics
- Spectroscopy
Background:
- Surface-enhanced Raman scattering (SERS) offers ultrasensitive molecular detection but relies heavily on controlled light-matter interactions.
- Gold nanoparticle films, anisotropic gold nanotriangles (AuNTs) and isotropic gold nanospheres (AuNSs), are key plasmonic materials.
- Fabry-Pérot (FP) cavities can tailor light-matter interactions for enhanced optical phenomena.
Purpose of the Study:
- To investigate the shape-dependent SERS enhancement of self-assembled gold nanoparticle films integrated with FP cavities.
- To explore the impact of modal ultrastrong coupling on SERS performance.
- To optimize SERS platforms for both analyte-rich and analyte-limited conditions.
Main Methods:
- Fabrication of self-assembled AuNT and AuNS films on semi-opened FP cavities with tunable TiO2 dielectric layers.
- Characterization of light-matter coupling using reflection spectroscopy and finite-difference time-domain (FDTD) simulations.
- Evaluation of SERS performance under varying analyte concentrations and TiO2 thicknesses.
Main Results:
- Modal ultrastrong coupling between nanoparticle plasmon modes and FP cavity modes was achieved, with peak splitting energy of ~650 meV.
- Shape-dependent SERS enhancement was observed, influenced by near-field intensity, hotspot distribution, and molecular accessibility.
- AuNT films demonstrated superior SERS signal quality and sensitivity under analyte-limited conditions compared to AuNS films.
Conclusions:
- Integrating self-assembled gold nanoparticle films with FP cavities enables tailorable SERS enhancement.
- Shape anisotropy of AuNTs is crucial for enhanced hotspot formation and efficient analyte access, leading to superior performance in analyte-limited scenarios.
- This approach offers a pathway for designing advanced SERS platforms for practical photonic and chemical sensing applications.
Keywords:
Fabry–Pérot cavitylocalized surface plasmon resonancemodal ultrastrong couplingself-assemblysurface-enhanced Raman scattering
