Refractive index biosensing using near-UV metal–dielectric–metal nanostructured arrays: fabrication and simulation

This work reports the design, simulation, and fabrication of a metal–dielectric–metal (MDM) nanohole array structure toward a realization of a refractive index biosensor. The MDM nanohole array structure operating near the UV range consists of a subwavelength hole array inscribed through the upper aluminum (Al) layer positioned on a stack of a thin silica (SiO2) spacer and an Al mirror on a silicon substrate. The quality factor of the resonance at ∼390nm of the present nanostructure is ∼1.5times higher than the previous result owing to the larger fill factor of Al material on the upper layer. This means at the UV range, the designed nanohole array structure closely resembles the dielectric gratings in the visible range. At resonance, we numerically observed a strong confinement of incident light localized inside the subwavelength apertures and the SiO2 spacer, and thus high absorption and directive emission of up to 99% and ∼8.0deg, respectively. The MDM nanohole array structure has been fabricated by using plasma-enhanced chemical vapor deposition combining with the focused ion beam, and its reflection experiments are in good agreement with the finite-difference time-domain simulation results. The proposed MDM nanohole array structure can be applicable for a wide variety of plasmonic sensing, in particular for refractive index biosensors. Because of working in the near-UV range, this refractive index biosensor shows the figure of merit to have a selectivity that is ∼4.0times higher than that of other established plasmonic MDM biosensors.