Surface-enhanced Raman scattering inducible by recyclable Ag-coated magnetic particles

A novel fabrication of Ag-deposited silica-coated Fe3O4 particles and their application as surface-enhanced Raman scattering (SERS) substrates in chemical analyses are demonstrated. Initially, 426-nm sized spherical magnetite particles composed of 13-nm-sized superparamagnetic Fe3O4 nanoparticles were synthesized, and silver coating was conducted using butylamine as the reductant of AgNO3 in ethanol, after direct silica coating on the Fe3O4 particles. The Ag-deposited silica-coated Fe3O4 particles (Fe3O4/SiO2@Ag) are found to be efficient SERS substrates with the enhancement factor at 632.8 nm excitation to be about 3 × 106. Since the magnetic particles are readily recovered from the solution phase without centrifugation and/or filtering, these SERS-active magnetic particles must be useful in the Raman spectroscopic analysis of dissolved organic species, as well as thin organic films. For instance, adenine could be detected down to 10 nM concentrations. In addition, an 1.5-nm thick dye film on a glass slide could also be detected by Raman spectroscopy after dropping 1.0 μL of Fe3O4@Ag colloids onto the film. The used Fe3O4/SiO2@Ag particles can then be recycled by treatment with a mild borohydride solution.