Magnetic and optical bifunctional nanoparticles that combine easy separation, preconcentration, and efficient SERS capabilities have been fabricated with high sensitivity and reproducibility through a low-cost method. These gold nanoparticles attached on magnetic silica-coated cobalt nanospheres (Co@SiO2/AuNPs) display the advantage of strong resonance absorption due to gaps at nanoscale between neighboring metal nanoparticles bringing large field enhancements, known as "hot spots". The prepared particles can be controlled by using an external magnetic field, which makes them very promising candidates in biological applications and Raman spectroscopic analysis of dissolved organic species. The magnetic property of the prepared particles lowers the detection limits through preconcentration with solid-phase extraction in SERS analysis. The performance of the prepared nanostructures was evaluated as a SERS substrate using brilliant cresyl blue (BCB) and rhodamine 6G (R6G) as model compounds. The solid-phase affinity extraction of 4-mercapto benzoic acid (4-MBA) using bifunctional Co@SiO2/AuNPs nanoparticles followed by magnetic separation and the measurement of the SERS signal on the same magnetic particles without elution were investigated. Approximately 50-fold increase in SERS intensity was achieved through solid-phase extraction of 8.3 x 10(-6) M 4-MBA in 10 min.