Exploring surface sensitivity of Rayleigh anomaly in metal/dielectric multilayer gratings

Biosensors based on Rayleigh anomaly (RA) in metal gratings exhibit impressive bulk refractive index (RI) sensitivity and narrow lincwidth. However, the electric field enhancement extends far away from surface of the gratings, which limits the application on biosensor Where the RI changes are restricted at the sensor interface. To overcome this shortcoming, a hovel grating composed of a 8-layer Au/Al2O3 stack was optimized by numerical simulation. The electric field is limited in several hundreds of nanometers from surface. The surface sensitivity increases 10 times than that of Au gratings at the detection depth of less than 400 nm. The surface index sensitivity can be improved 5 times under oblique incidence than that under normal incidence when the thickness of cover media is 20 nm. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement