Fabrication and Numerical Characterization of Infrared Metamaterial Absorbers for Refractometric Biosensors

We report the successful fabrication of infrared plasmonic metamaterial absorbers by electron beam lithography and the lift-off technique. The absorber consists of periodic arrays of gold (Au) nanostructures deposited on a stack of thin silica spacer and gold film (acting as a mirror) on a silicon wafer. At resonance, we numerically observed a strong field enhancement between the metallic nanostructures and the Au film, resulting in a strong confinement of incident light within the silica spacer and thus a high absorption of up to 80% at infrared wavelengths. Our experimental measurement for reflection coefficients are in excellent agreement with the full-wave simulation results. We show that the resonant absorption spectral response can be used for highly-sensitive, label-free refractive-index biosensors. By tailoring various forms of nanostructures, we investigate their refractive index sensitivities to identity the most sensitive sensor at specific infrared wavelengths.