Spatially Uniform and Quantitative Surface-Enhanced Raman Scattering under Modal Ultrastrong Coupling Beyond Nanostructure Homogeneity Limits

We developed a substrate that enables highly sensitive and spatially uniform surface-enhanced Raman scattering (SERS). This substrate comprises densely packed gold nanoparticles (d-AuNPs)/titanium dioxide/Au film (d-ATA). The d-ATA substrate demonstrates modal ultrastrong coupling between localized surface plasmon resonances (LSPRs) of AuNPs and Fabry–Pérot nanocavities. d-ATA exhibits a significant enhancement of the near-field intensity, resulting in a 78-fold increase in the SERS signal for crystal violet (CV) compared to that of d-AuNP/TiO2 substrates. Importantly, high sensitivity and a spatially uniform signal intensity can be obtained without precise control of the shape and arrangement of the nanoscale AuNPs, enabling quantitative SERS measurements. Additionally, SERS measurements of rhodamine 6G (R6G) on this substrate under ultralow adsorption conditions (0.6 R6G molecules/AuNP) show a spatial variation in the signal intensity within 3%. These findings suggest that the SERS signal under modal ultrastrong coupling originates from multiple plasmonic particles with quantum coherence

Photo-induced fluorescence emission enhancement of azobenzene thin films

UV irradiation-induced fluorescence enhancement of thin films composed of azobenzene amphiphiles, C12AzoC10N+ (AzoN+), was investigated. UV irradiation to Langmuir-Blodgett (LB) monolayers of AzoN+ indicated that the fluorescence emission from an irradiated area was enhanced and the emission was independent of the aggregation structures of an azobenzene moiety. Moreover, UV irradiation to cast films of AzoN+ revealed that the enhancement was increased by increasing the irradiation time. The fluorescence by excitation at 365 nm occurred over a wide range of wavelengths from around 400 nm to 650 nm, and the emission was not attributed to the J aggregates of AzoN+. he mechanism for this phenomenon has not been elucidated. It may be caused by the photo-chemical reaction of the azobenzene moiety or photo-induced specific aggregates. However, UV irradiation-induced fluorescence enhancement can be applicable to optical memory devices

Salt-triggered Active Plasmonic Systems Based on the Assembly/Disassembly of Gold Nanorods in a DNA Brush Layer on a Solid Substrate

In this study, we demonstrate that the plasmonic properties of gold nanorods (GNRs) electrostatically adsorbed on a DNA brush substrate are reversibly controlled by changes in NaCl concentration. This plasmonic change results from GNR assembly/disassembly in a DNA brush layer. In addition, we show that this active plasmonic system exhibits intense and switchable chiroptical properties