Sensitivity enhancement of plasmonic grating in the local field

A plasmonic grating consisting of parallel gold or silver nanowires on the glass substrate is an excellent sensor for refractive index measurement of a gas or liquid medium. We suggest measuring the local field in a gap between the wires to increase the sensitivity. The local electric field contains more information on the environment since it includes the evanescent waves. Calculation by the boundary element method confirms a substantial improvement of sensitivity owing to a sharp cusp-like gap resonance in the angular dependence. The local field measurement under the frustration of total internal reflection has promising prospects for the development of modern biomedical and chemical sensors.