We　present　a　simple　and　robust　structure　to　realize　Fano　resonance　for　refractive　index　sensing　applications.　The　Fano　resonance　with　ultrahigh　Q　factors　(Q　＞　5.0　x　10(4))　and　high　reflections　(near　100%)　is　realized　in　a　2-D　defect-free　pillar　array　photonic　crystal　(PAPC)　with　optimized　geometry　(e.g.,　pillar　array　periodicity,　height,　and　radius).　We　analyze　its　band　structure,　polarization,　and　transmission　characteristics　in　detail　with　numerical　methods　(plane　wave　expansion　and　3-D　finite-difference　time-domain　(3-D-FDTD)　simulations).　The　numerical　results　show　that　FOM　similar　to　6.85　x　10(3)　(FOM　being　the　figure　of　merit)　can　be　achieved,　which　is　an　order　of　magnitude　improved　over　the　previous　work.　In　addition,　the　unique　simplicity　of　this　system　in　which　a　long-lifetime　delocalized　electromagnetic　field　exists　and　interacts　with　the　surrounding　media　permits　new　opportunities　for　point-of-care　applications.　Furthermore,　the　proposed　architecture　makes　the　implementation　of　lab-on-a-chip　refractive　index　sensing　possible,　which　is　enabled　by　integrating　PAPC　on　the　tip　of　an　optical　fiber.