This　study　proposes　a　facile　method　for　synthesis　of　Au　coated　magnetic　nanoparticles　(AuMNPs)　core/shell　nanocomposites　with　nanoscale　rough　surfaces.　MnFe2O4　nanoparticles　(NPs)　were　first　modified　with　a　uniform　polyethylenimine　layer　(2　nm)　through　self　assembly　under　sonication.　The　negatively　charged　Au　seeds　were　then　adsorbed　on　the　surface　of　the　MnFe2O4　NPs　through　electrostatic　interaction　for　Au　shell　formation.　Our　newly　developed　sonochemically　assisted　hydroxylamine　seeding　growth　method　was　used　to　grow　the　adsorbed　gold　seeds　into　large　Au　nanoparticles　(AuNPs)　to　form　a　nanoscale　rough　Au　shell.　Au-coated　magnetic　nanoparticles　(AuMNPs)　were　obtained　from　the　intermediate　product　(Au　seeds　decorated　magnetic　core)　under　sonication　within　5　min.　The　AuMNPs　were　highly　uniform　in　size　and　shape　and　exhibited　satisfactory　surface-enhanced　Raman　scattering　(SERS)　activity　and　strong　magnetic　responsivity.　PATP　was　used　as　a　probe　molecule　to　evaluate　the　SERS　performance　of　the　synthesized　AuMNPs　with　a　detection　limit　of　10(-9)　M.　The　synthesized　AuMNPs　were　conjugated　with　Staphylococcus　aureus　(S.　aureus)　antibody　for　bacteria　capture　and　separation.　The　synthesized　plasmonic　AuNR-DTNB　NPs,　whose　LSPR　wavelength　was　adjusted　to　the　given　laser　excitation　wavelength　(785　nm),　were　conjugated　with　S.　aureus　antibody　to　form　a　SERS　tag　for　specific　recognition　and　report　of　the　target　bacteria.　S.　aureus　was　indirectly　detected　through　SERS　based　on　sandwich-structured　immunoassay,　with　a　detection　limit　of　10　cells/mL.　Moreover,　the　SERS　intensity　at　Raman　peak　of　1331　cm(-1)　exhibited　a　linear　relationship　to　the　logarithm　of　bacteria　concentrations　ranging　from　10(1)　cells/mL　to　10(5)　cells/mL.