3D-FDTD modelling of optical biosensing based on gold-coated nanoporous anodic alumina

Abstract The suitability of using gold-coated nanoporous anodic alumina structures as a platform for reflectometry-based plasmonic biosensors is investigated by numerical simulation. Reflectance spectra of such structures has been obtained using 3D-FDTD while the sensing capabilities have been evaluated as the change in spectra upon the adsorption of a layer of a biological-related molecule (biolayer) on the gold coating and inner pore surface. Results show that the gold-coated nanoporous structure enables the coupling of normally incident light to a localized surface plasmon resonance, and that such resonance shifts upon the adsorption of the biolayer. A sensitivity can be defined as the resonance wavelength shift with the biolayer refractive index. It is demonstrated that smaller gold coating thicknesses result in an increase in sensitivity, but at the cost of a decrease in the resonance sharpness, what suggests the existence of an optimal gold coating thickness.