Abstract
Surface plasmon resonance (SPR) sensors detect refractive index changes on metal thin films and are frequently used in aqueous solutions as bio- and chemical-sensors. Recently, we proposed new SPR sensors using aluminum (Al) thin films that work in the far- and deep-ultraviolet (FUV-DUV, 120–300 nm) regions and investigated SPR properties by an attenuated total reflectance (ATR) based spectrometer. The FUV-DUV-SPR sensors are expected to have three advantages compared to visible-SPR sensors: higher sensitivity, material selectivity, and surface specificity. However, in this study, it was revealed that the Al thin film on a quartz prism cannot be used as the FUV-DUV-SPR sensor in water solutions. This is because its SPR wavelength shifts to the visible region owing to the presence of water. On the other hand, the SPR wavelength of the Al thin film on the sapphire prism remained in the DUV region even in water. In addition, the SPR wavelength shifted to longer wavelengths with increasing refractive index on the Al thin film. These results mean that the Al thin film on the sapphire prism can be used as the FUV-DUV-SPR sensor in solutions, which may lead to the development of novel and sophisticated SPR sensors.
Highlights
Surface plasmon resonance (SPR) sensors detect refractive index changes near the surface of a metal thin film as changes in the intensity of reflected light, which are induced by SPR wavelength and angle shifts
The present Al thin film on the sapphire prism showed the red-shift of the SPR wavelength in the DUV region on increasing the concentration of the sucrose water solution, which may lead to the development of the FUV-DUV-SPR sensor working in the solutions
The Al-SPR wavelength dependence on the refractive indices of the prisms and the materials placed on the Al thin film were systematically investigated
Summary
SPR properties of the Al film on the quartz prism. Figure 1a shows the reflection spectra in the 170–. Al was evaporated on the trapezoid sapphire prism instead of the quartz prism, and the reflectance spectra in the 170–300 nm region were measured in HFIP and water (Fig. 1c). These liquids were selected because they have little absorbance in the measurement wavelength, which makes it easier to discuss the refractive index dependence of the SPR. According to simulations based on the Fresnel equations, an Al film on a sapphire prism in air has no SPR absorbance and has almost constant reflectance intensity in the 180–300 nm region at a 70° incident angle (Fig. 1d, black line). In the present study, the reflection spectrum in the air can be used as the reference to determine the SPR wavelength with materials on the Al film
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