  In this paper, we present a plasmonic refractometric sensor that works under
normal incidence; allowing its integration on a fiber tip. The sensor's
material and geometry exploit the large scattering cross-section given by
high-contrast of the index of refraction subwavelength dielectric gratings. Our
design generates a hybrid plasmonic-Fano resonance due to the interference
between the surface plasmon resonance and the grating response. We optimize the
sensor with a merit function that combines the quality parameter of the
resonance and the field enhancement at the interaction volume where the plasmon
propagates. Our device shows a high sensitivity (1000 nm/RIU) and a high Figure
of Merit (775 RIU$^{-1}$). Degradation in performance is negligible through a
wide dynamic range up to 0.7 RIU. These quantitative parameters overperform
compared to similar plasmonic sensors.
