A　magnetically　assisted　surface-enhanced　Raman　scattering　(SERS)　biosensor　for　single-cell　detection　of　S.　aureus　on　the　basis　of　aptamer　recognition　is　reported　for　the　first　time.　The　biosensor　consists　of　two　basic　elements　including　a　SERS　substrate　(Ag-coated　magnetic　nanoparticles,　AgMNPs)　and　a　novel　SERS　tag　(AuNR-DTNB@AgDTNB　core-shell　plasmonic　NPs　or　DTNB-labeled　inside-and-outside　plasmonic　NPs,　DioPNPs).　Uniform,　monodisperse,　and　superparamagnetic　AgMNPs　with　favorable　SERS　activity　and　magnetic　responsiveness　are　synthesized　by　using　polymer　polyethylenimine.　AgMNPs　use　magnetic　enrichment　instead　of　repeated　centrifugation　to　prevent　sample　sedimentation.　DioPNPs　are　designed　and　synthesized　as　a　novel　SERS　tag.　The　Raman　signal　of　DioPNPs　is　10　times　stronger　than　that　of　the　commonly　used　SERS　tag　AuNR-DTNB　because　of　the　double-layer　DTNB　and　the　LSPR　position　adjustment　to　match　the　given　laser　excitation　wavelength.　Consequently,　a　strong　SERS　enhancement　is　achieved.　Under　the　optimized　aptamer　density　and　linker　length,　capture　by　aptamer-modified　AgMNPs　can　achieve　favorable　bacteria　arrest　(up　to　75%).　With　the　conventional　Raman　spectroscopy,　the　limit　of　detection　(LOD)　is　10　cells/mL　for　S.　aureus　detection,　and　a　good　linear　relationship　is　also　observed　between　the　SERS　intensity　at　Raman　peak　1331　cm(-1)　and　the　logarithm　of　bacteria　concentrations　ranging　from　10(1)　to　10(5)　cells/mL.　With　the　help　of　the　newly　developed　SERS　mapping　technique,　single-cell　detection　of　S.　aureus　is　easily　achieved.