Enhanced Surface Plasmon Resonance Wavelength Shifts by Molecular Electronic Absorption in Far- and Deep-Ultraviolet Regions

Ichiro Tanabe,Koji Watari,Yoshito Y Tanaka,Wataru Inami,Yoshimasa Kawata,Yukihiro Ozaki

doi:10.1038/s41598-020-66949-z

Abstract

In this study, surface plasmon resonance (SPR) wavelength shifts due to molecular electronic absorptions in the far-ultraviolet (FUV, < 200 nm) and deep-ultraviolet (DUV, < 300 nm) regions were investigated by attenuated total reflectance (ATR) spectroscopy. Due to the strong absorption in the DUV region, N,N-dimethylformamide (DMF) significantly increased the SPR wavelength shift of Al film. On the other hand, no such shift enhancement was observed in the visible region for Au film because DMF does not have absorbance compared to non-absorbing materials such as water and alcohols. The enhanced SPR wavelength shift, caused by the overlap between SPR and molecular resonance wavelengths in FUV-DUV region, is expected to result in high sensitivity for resonant materials.

Highlights

An surface plasmon resonance (SPR) sensor, which detects refractive index changes near the surface of a metal film, is one of the most important and typical SPR-based applications and is widely used in biochemistry and environmental chemistry[16,17,18,19,20]
The effects of molecular electronic absorptions on SPR sensing were probed by casting liquid samples (1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), water, 2-propanol, 2-butanol, 1-octanol, N,N-dimethylformamide (DMF), and HFIP/DMF mixtures) on an Al film deposited on a sapphire prism
The refractive index n of the environment close to the Al film surface was tuned by casting of HFIP, water, 2-propanol, 2-butanol, and 1-octanol one by one

Summary

Introduction

An SPR sensor, which detects refractive index changes near the surface of a metal film, is one of the most important and typical SPR-based applications and is widely used in biochemistry and environmental chemistry[16,17,18,19,20]. The SPR properties of Al films in the FUV region have been studied since the 1970’s32–34, their dependence on the refractive index and FUV-DUV-SPR sensor operation have not been described yet This is because even O2 and H2O molecules strongly absorbed light in the FUV region and the investigations had to be performed in a high vacuum atmosphere[32,33,34]. It was revealed that, due to the strong electronic absorptions of DMF (i.e., anomalous dispersion of the refractive index n) near the SPR wavelength, the SPR shift was significantly enhanced compared to the other samples which had no absorbance. Such enhancements were not induced in the Au-based visible-SPR sensor. These results indicate that the selection of a specific light absorption wavelength of the target material allows its selective detection due to the marked changes of n, which is the advantage the FUV-DUV-SPR sensor

Methods

Results

Conclusion