We　investigate　the　spectroscopic　response　of　Rayleigh　anomaly　in　a　dielectric　grating　before　and　after　it　is　coated　with　a　layer　of　aluminum.　The　metallic　coating　enabled　effective　prohibition　of　the　diffractions　into　the　substrate　and　suppressed　the　background　of　the　optical　extinction　spectrum　of　Rayleigh　anomaly.　This　enhanced　significantly　both　the　contrast　and　the　amplitude　of　the　sensor　signal　based　on　the　spectral　shift　of　Rayleigh-anomaly.　Sensor　measurements　were　performed　on　the　glucose/water　solutions　with　different　concentrations,　which　show　improved　performance　due　to　the　enhancement　of　the　spectral　contrast.　(C)　2016　Optical　Society　of　America