Abstract
We show here the design, fabrication, and characterization of a wedge-shaped Au thin film with an enhanced figure of merit (FOM). This is achieved by using a reflectivity change in an attenuated total reflection (ATR) setup by slightly modulating the wavenumber of the surface plasmon polariton by means of the varying thickness of the Au thin film. The wedge-shaped Au thin film is equivalent to multiple surface plasmon resonance (SPR) transducers integrated in a single chip and was fabricated by an electron-beam evaporation process with the position of the shutter controlled during the deposition. The FOM, defined as the difference between the maximum and minimum values of the normalized reflectivity change (ΔR/R) divided by the corresponding difference of the incident angles, was 8.0-times larger than that based on the reflectivity R. Also, we demonstrated that the wedge-shaped Au thin film was able to detect ethanol gas at a concentration of 0.2%, corresponding to a refractive index change of 2 × 10−5, without any surface functionalization. Since the sensing signal can be obtained with a single image from the wedge-shaped Au thin film without precise thickness control of the metal thickness, no other materials or modulation equipment is necessary, and the sensing chip can be employed in simple and highly sensitive systems.
Highlights
Surface plasmon resonance (SPR) sensors are powerful tools for real-time highly sensitive and labelfree detection of analytes with a small size and high throughput, and have been applied to biomolecule detection by monitoring the change in the refractive index (RI) on the metal surface (Liedberg et al, 1983; Liedberg et al, 1995; Homola et al, 1999; Phillips, 2008)
A lot of approaches have been studied in SPR sensors built on propagating plasmonic eigenwave, surface plasmon polariton (SPP), or localized plasmonic eigenmode, localized surface plasmon resonance (LSPR)
The figure of merit (FOM), based on the reflectivity change ΔR/R of the wedge-shaped Au thin film, was 8.0 times larger than that based on the reflectivity R
Summary
Surface plasmon resonance (SPR) sensors are powerful tools for real-time highly sensitive and labelfree detection of analytes with a small size and high throughput, and have been applied to biomolecule (protein, DNA) detection by monitoring the change in the refractive index (RI) on the metal surface (Liedberg et al, 1983; Liedberg et al, 1995; Homola et al, 1999; Phillips, 2008). A Wedge-Shaped Au Thin Film sensitivity, signal-to-noise ratio (SNR), and limit of detection (LOD). For these modulation configurations, external modulators are necessary leading to large-size, high-cost, and complex sensor systems. Small-size, lowcost, and simple SPR sensors without precise thickness of control of the metal film are desired. Reports on SPR sensors satisfying these demands are limited
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