Hollow　core　anti-resonant　fiber　(HARE)　has　found　a　handful　applications　in　optical　communications,　nonlinear　optics　and　high　power　delivery.　The　intrinsic　property　of　the　fiber　also　renders　it　an　ideal　candidate　for　biosensing,　which　has　not　been　explored　intensively.　Herein,　we　demonstrate　an　optical　fiber　sensing　platform,　taking　advantages　of　the　state-of-the-art　HARP　technology　and　superior　physicochemical　properties　of　2D　material　black　phosphorus,　for　ultra-sensitive　detection　of　bisphenol　A　(BPA)　in　blood　and　environmental　samples.　The　specially　designed　HARP　can　not　only　achieve　broadband　transmission　of　light,　but　also　confine　light　in　the　low　refractive-index　liquid　core,　ensuring　maximum　overlap　of　light　and　liquid　core.　Modification　of　the　inner　surface　of　HARP　with　2D　black　phosphorus　nanoflakes　functionalized　with　fluorescently　labeled　BPA-specific　aptamer　provides　a　smart　sensing　interface　enabling　highly　selective　detection　of　BPA　via　measuring　the　fluorescence.　The　limit　of　detection　is　1.69pM,　which　is　more　than　two　orders　of　magnitude　enhancement　compared　to　the　conventional　plate　assay.　The　proposed　assay　is　not　interfered　with　the　BPA　analogues　BPB　and　BPS.　The　long　optical　path　with　tight　optical　confinement　greatly　enhances　the　analyte-light　interaction　and　improves　the　sensitivity　of　the　sensing　platform.　The　proposed　sensing　platform　can　be　further　developed　for　versatile　applications.