Localized　surface　plasmon　resonance　(LSPR)-based　sensors　exhibit　enormous　potential　in　the　areas　of　medical　diagnosis,　food　safety　regulation　and　environmental　monitoring.　However,　the　broadband　spectral　lineshape　of　LSPR　hampers　the　observation　of　wavelength　shifts　in　sensing　processes,　thus　preventing　its　widespread　applications　in　sensors.　Here,　we　describe　an　improved　plasmonic　sensor　based　on　Fano　resonances　between　LSPR　and　the　Rayleigh　anomaly　(RA)　in　a　metal–insulator–metal　(MIM)　meta-grating,　which　is　composed　of　silver　nanoshell　array,　an　isolation　grating　mask　and　a　continuous　gold　film.　The　MIM　configuration　offers　more　freedom　to　control　the　optical　properties　of　LSPR,　RA　and　the　Fano　resonance　between　them.　Strong　couplings　between　LSPR　and　RA　formed　a　series　of　narrowband　reflection　peaks　(with　a　linewidth　of　~20　nm　in　full　width　at　half　maximum　(FWHM)　and　a　reflectivity　nearing　100%)　within　an　LSPR-based　broadband　extinction　window　in　the　experiment,　making　the　meta-grating　promising　for　applications　of　high-efficiency　reflective　filters.　A　Fano　resonance　that　is　well　optimized　between　LSPR　and　RA　by　carefully　adjusting　the　angles　of　incident　light　can　switch　such　a　nano-device　to　an　improved　biological/chemical　sensor　with　a　figure　of　merit　(FOM)　larger　than　57　and　capability　of　detecting　the　local　refractive　index　changes　caused　by　the　bonding　of　target　molecules　on　the　surface　of　the　nano-device.　The　figure　of　merit　of　the　hybrid　sensor　in　the　detection　of　target　molecules　is　6　and　15　times　higher　than　that　of　the　simple　RA-　and　LSPR-based　sensors,　respectively.　©　2023　by　the　authors.