Abstract
A design study of a nanostructured two-dimensional plasmonic crystal based on aluminum and polymeric material for label-free optical biosensing is presented. The structure is formed of Al nanohole and nanodisk array layers physically separated by a polymeric film. The photonic configuration was analyzed through finite-difference time-domain (FDTD) simulations. The calculated spectral reflectance of the device exhibits a surface plasmon polariton (SPP) resonance feature sensitive to the presence of a modeled biolayer adhered onto the metal surfaces. Simulations also reveal that the Al disks suppress an undesired SPP resonance, improving the device performance in terms of resolution as compared to that of a similar configuration without Al disks. On the basis of manufacturability issues, nanohole diameter and depth were considered as design parameters, and a multi-objective optimization process was employed to determine the optimum dimensional values from both performance and fabrication points of view. The effect of Al oxidation, which is expected to occur in an actual device, was also studied.
Highlights
Plasmonic devices based on metal nanostructures can concentrate and enhance light in their near surroundings, which may be exploited to increase light–matter interaction in nanoscale spatial regions [1]
We decided to operate the biosensor in air because it should be more sensitive in this medium than immersed in a liquid: refractive index changes caused by molecular adsorption are larger in air than in liquids [10]
We have considered that the measurement of the full width at half maximum (FWHM) is not an issue because this value is typically larger than a few nanometers for the studied configuration and can be measured by cost-effective compact spectrometers
Summary
Plasmonic devices based on metal nanostructures can concentrate and enhance light in their near surroundings, which may be exploited to increase light–matter interaction in nanoscale spatial regions [1] This remarkable property has enabled the development of highly sensitive label-free optical biosensors [2,3] based on either the sensitivity of surface plasmon polariton (SPP) and/or localized surface plasmon (LSP) resonances to changes of the refractive index at metal/dielectric interfaces, or Raman signal amplification due to SP electromagnetic field enhancement (surface-enhanced Raman spectroscopy). One of these alternative materials, Sensors 2018, 18, 3335; doi:10.3390/s18103335 www.mdpi.com/journal/sensors
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