Surface　enhanced　Raman　scattering　(SERS)　spectroscopy　is　a　widely　used　analytical　technique　for　detecting　chemicals　or　biological　molecules　with　high　sensitivity　and　high　specificity.　Enhancing　the　sensitivity　and　lowering　the　detection　limits　are　always　the　working　direction　of　this　research　field.　Furthermore,　direct　detection　of　low-concentration　molecules　in　liquids　remains　a　big　challenge.　In　this　work,　we　construct　a　SERS　device　consisting　of　periodically　arranged　polylactic　acid　(PLA)　lines　that　are　coated　with　silver,　where　the　PLA　line　array　is　produced　by　3D　printing　technique.　The　plasmonic　nanogroove　within　the　gap　between　the　two　adjacent　PLA　lines　is　found　to　be　the　dominant　mechanism　for　SERS　detection.　A　maximum　enhancement　factor　of　2.26　x　106　has　been　achieved　for　the　plasmonic　nanogroove,　with　respect　to　a　pure　planar　glass　substrate.　A　detection　limit　of　lower　than　0.5　ppm　has　been　research　for　such　a　sensor　device　in　the　direct　detection　of　melamine　in　its　aqueous　solution.　Furthermore,　the　PLA　lines　have　advantages　of　biodegradability,　biocompatibility,　low　costs,　and　thermo-plasticity,　making　the　device　environmentally　friendly　in　potential　applications　in　food　safety　inspection　and　pollutant　detection　in　water.