Raman optical activity (ROA) is a powerful tool for identifying the absolute conformational information and behavior of chiral molecules in aqueous solutions, but suffers from low sensitivity. Here we report our development of a silicon nanodisk array that tailors a chiral field to significantly increase the interaction between the excitation light and chiral molecules via exploiting a dark mode. Specifically, we used the array with pairs of chemical and biological enantiomers to show >100x enhanced chiral light-molecule interaction with negligible artifacts for ROA measurements. Our silicon nanodisk array opens a cost-effective way for conformational analysis of trace chiral molecules.
Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for vibrational spectroscopy, but is compromised by its low reproducibility, uniformity, biocompatibility, and durability. This is because it depends on “hot spots” for high signal enhancement. Here we report our experimental demonstration of a plasmon-free nanostructure composed of a two-dimensional array of porous carbon nanowires as a SERS substrate for highly sensitive, biocompatible, and reproducible SERS. Specifically, the substrate provides not only high signal enhancement, but also high reproducibility and fluorescence quenching capability. We experimentally demonstrated these excellent properties with various molecules such as rhodamine 6G (R6G), β-lactoglobulin, and glucose.
Spectroscopy of near-single molecular surface enhanced resonant Raman scattering (SERRS) of single plasmonic nanoparticle (NP) systems like NP dimer revealed that such systems are in strong coupling regimes between plasmon resonance and molecular exciton. We firstly show the evidence of strong coupling between plasmon and molecular exciton by calculation of classical electromagnetism. Secondly, we show reproduction of SERRS with surface enhanced fluorescence (SEF) spectra of dye molecules in the gaps of dimers under strong coupling conditions. By the way, the electronic structure of molecules in the strong coupling system is expected to be modulated by vacuum electromagnetic fields under the near single dye molecule condition. Thus, we finally show absorption spectroscopy of single strong coupling systems by combining extinction with scattering spectroscopy.
Tip-enhanced Raman scattering (TERS) can be observed highly sensitive spectral image with high spatial resolution.
However, it shows low reproducibility due to difference and change in optical properties of the metallic tips. For surfaceenhanced
Raman scattering (SERS), the spectra can be reproduced by the scattering spectra due to localized surface
plasmon resonance (LSPR) of the individual metallic nanostructures, which observed with a dark field illumination, and
the calculated electromagnetic field around the nanostructures. In the present study, we tried to relate TERS spectra with
the LSPR spectra and the calculation, in a similar way of SERS. By conventional dark field illumination, LSPR
scattering spectra at the apex of the tip were measured and were compared with the corresponding TERS spectra. By
excitation using polarization parallel to the tip, the polarized LSPR peak was stronger than that by perpendicular
polarization. Also in the case of TERS, the similar trend was observed. It was confirmed whether the vertical
polarization to the sample plane (Z-polarization) is effective or not by the polarized LSPR and TERS spectra. By
excitation at different wavelengths, moreover, TERS enhancement factors were compared. In the calculation for TERS,
the nanostructure like a monopole antenna was adopted, because the EM field is enhanced not at both sides, but at only
apex. The dependence on taper and curvature of the tip were compared with the calculated results for the nanostructure
like a conventional dipole antenna.
When near-infrared laser was focused in colloidal silver, not only optical trapping of silver nanoparticles, but also hyper-Rayleigh scattering were observed at the laser focus. By addition of NaCl and rhodamine 6G in the colloidal silver, hyper-Rayleigh scattering was enhanced and hyper-Raman scattering was also observed. These nonlinear optical responses showed temporal fluctuation in spite of the continuous laser irradiation. Experimental results suggested that aggregates which have a high activity for nonlinear optical responses were trapped and/or produced by a focusing near-infrared laser. Hyper-Raman signal, whose scattering cross section is much lower than normal Raman scattering, could be obtained easily by focusing a cw-YAG laser in colloidal silver including analytes. It was demonstrated that optical trapping of colloidal silver is a powerful technique to obtain the nonlinear optical responses.
Conference Committee Involvement (6)
Enhanced Spectroscopies and Nanoimaging 2025
3 August 2025 | San Diego, California, United States
Enhanced Spectroscopies and Nanoimaging 2024
18 August 2024 | San Diego, California, United States
Enhanced Spectroscopies and Nanoimaging 2023
20 August 2023 | San Diego, California, United States
Enhanced Spectroscopies and Nanoimaging 2022
21 August 2022 | San Diego, California, United States
Enhanced Spectroscopies and Nanoimaging 2021
2 August 2021 | San Diego, California, United States
Enhanced Spectroscopies and Nanoimaging 2020
24 August 2020 | Online Only, California, United States
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