Gold-Assembled Silica-Coated Cobalt Nanoparticles as Efficient Magnetic Separation Units and Surface-Enhanced Raman Scattering Substrate Lütfiye Sezen Yildirim1,, Murat Kaya2,∗,, Mürvet Volkan

Abstract

Magnetic and optical bifunctional nanoparticles that combine easy separation, preconcentration, and efficientSERS capabilities have been fabricated with high sensitivity and reproducibility through a low-cost method. Thesegold nanoparticles attached on magnetic silica-coated cobalt nanospheres (Co@SiO2 /AuNPs) display the advantageof strong resonance absorption due to gaps at nanoscale between neighboring metal nanoparticles bringing large fieldenhancements, 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 dissolvedorganic species. The magnetic property of the prepared particles lowers the detection limits through preconcentrationwith solid-phase extraction in SERS analysis. The performance of the prepared nanostructures was evaluated as a SERSsubstrate using brilliant cresyl blue (BCB) and rhodamine 6G (R6G) as model compounds. The solid-phase affinityextraction of 4-mercapto benzoic acid (4-MBA) using bifunctional Co@SiO2 /AuNPs nanoparticles followed by magneticseparation 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 × 10 −6 M 4-MBAin 10 min.