Organic　molecules,　including　the　benzene　series,　have　been　identified　as　pollutants　in　environmental　water.　Due　to　their　very　low　solubility,　they　have　very　small　concentrations　in　water,　and　they　are　difficult　to　be　detected　by　conventional　techniques.　In　particular,　there　is　a　lack　of　real-time,　accurate,　and　rapid　detection　methods　for　such　molecules　in　water.　However,　they　are　detrimental　to　human　health　in　many　aspects.　Toluene　has　been　an　important　indicator　of　such　environmental　pollution　detections.　In　this　work,　we　propose　a　3D　SERS　scheme　consisting　of　a　hollow　fiber　that　is　coated　on　the　inner　wall　with　densely　arranged　silver　nanoparticles,　which　supplies　multifold　Raman　enhancement　by　the　plasmonic　microcavity.　Strong　confinement　of　excitation　laser　energy　and　strongly　enhanced　Raman　signals　with　the　bidirectional　collection　are　utilized　to　achieve　high-sensitivity　detection　of　toluene　molecules　in　water.　Raman　signal　with　a　reasonable　signal-to-noise　ratio　has　been　measured　for　a　concentration　of　0.53　mg/L,　indicating　a　detection　limit　even　lower　than　this　value　for　such　a　Raman　spectroscopic　technique.　The　corresponding　enhancement　factor　is　higher　than　6　x　10(3)　with　respect　to　the　available　systems.　Thus,　this　device　not　only　enables　direct　trace　detection　and　real-time　monitoring　of　the　water-polluting　status　by　organic　molecules　but　also　supplies　a　practical　approach　for　biological　sensing.