Sensitive surface enhanced Raman spectroscopy (SERS) detection of methotrexate by core-shell-satellite magnetic microspheres.

An effective approach for fabricating core-shell-satellite magnetic microspheres was developed to form a sub-10nm positively charged mesoporous silica (mSiO2) interlayer, which was applied to enrich samples and create sufficient hotspots between the inner Fe3O4@Ag core and outer assembled gold nanoparticles (AuNPs) satellites. Based on the prepared Fe3O4@Ag/mSiO2/AuNPs (FASA) as SERS substrates, a sensitive and label-free detection of methotrexate in serum was successfully realized. The positively charged mSiO2 interlayer exhibited strong capability in enriching methotrexate through the electrostatic interaction. The intraparticle plasmonic coupling between the inner Ag shell and the outside AuNPs satellites, and magnetism-induced aggregation greatly enhanced the SERS activity of methotrexate. The diluted serum containing different concentrations of methotrexate was employed as real samples and the minimum detected concentration of methotrexate was as low as 1nM with a linear response range from 1 to 200nM. This sensitive and label-free SERS detection of methotrexate based on FASA offers great potential for practical applications in medicine and biotechnology.