FBS Colloquia No.411Nano-Biophotonics Group

Enhanced Raman Spectroscopy Using Fano Resonance

Raman spectroscopy is a technique that enables non-invasive analysis of chemical composition and molecular structure, and is widely applied in various fields ranging from physical and chemical analysis to the measurement of dynamic processes in living cells. In this technique, excitation light is irradiated onto a sample, and the Raman scattered light emitted from the sample is spectroscopically measured. However, since Raman scattered light is inherently very weak, signal enhancement is essential. To date, surface-enhanced Raman scattering (SERS) utilizing localized surface plasmon resonance excited by metal nanostructures has been widely used. However, in SERS, the enhancement intensity strongly depends on the shape and arrangement of the nanostructures, making it difficult to theoretically predict and control the enhancement intensity and its spatial distribution. In particular, the inhomogeneity of the enhancement poses a major constraint for imaging applications. In contrast, by utilizing propagating surface plasmon resonance excited on a flat metal thin film, a more uniform enhancement field can be expected. In our laboratory, with the aim of further enhancing the enhancement factor, we are developing a new surface-enhanced Raman spectroscopy method that utilizes Fano resonance. This method is achieved by stacking multiple dielectric layers on a metal thin film and coupling the propagating surface plasmon resonance with the guided-wave mode excited in the dielectric layers. In this colloquium, we will introduce the principles and research results of this Fano resonance-based surface-enhanced Raman spectroscopy.