Fundamental characteristics of remote plasmonic-enhanced Raman spectroscopy without close contact between analyte and metallic nanostructure

Abstract

Raman spectroscopy is a technique that can visualize various molecular information noninvasively without the need for invasive pretreatment of samples such as staining. However, Raman scattering light is very weak, and thus Raman spectroscopy has limitations in terms of molecular sensitivity and measurement time. One solution to overcome the problem of weak signal intensity is optical enhancement based on the plasmon resonance effect. Surface-enhanced Raman scattering (SERS) spectroscopy enables highly sensitive Raman spectroscopy owing to the enhancing near-field produced by plasmon resonance. This enhancing field is formed in an area of about 10 nm around the metallic nanostructures. However, the direct contact between the metallic nanostructures and the analyte molecules causes denaturation of the metallic nanostructures and the analyte molecules themselves, limiting the Raman spectroscopic analysis and its applications. In the present study, we developed a remote plasmonic enhancement (RPE) method, which is expected to provide a high enhancement by plasmon-molecule remote coupling via a silica columnar structure of several tens nm in size to a metallic nanostructure. We demonstrated that the RPE could be applied to Raman spectroscopy (RPERS, remote plasmonic-enhanced Raman spectroscopy). We have confirmed the high enhancement of more than 104 by RPERS and clarified the fundamental characteristics of the RPERS.