Silanization of Ag-Deposited Magnetite Particles: An Efficient Route to Fabricate Magnetic Nanoparticle-Based Raman Barcode Materials

Silica-coated Ag nanostructures usable as magnetic nanoparticle-based Raman barcode materials were developed. Initially, 283 nm sized spherical magnetite particles composed of 13 nm sized superparamagnetic Fe3O4 nanoparticles were synthesized, and silver deposition was conducted using butylamine as the reductant of AgNO3 in ethanol. The Ag-deposited Fe3O4 (Fe3O4@Ag) particles are found to be efficient surface-enhanced Raman scattering (SERS) substrates with the enhancement factor at 632.8 nm excitation to be about 3 x 10(6). After SERS markers such as benzenethiol, 4-mercaptotoluene, 4-aminobenzenethiol, and 4-nitrobenzenethiol were adsorbed onto the silver surface, poly(allylamine hydrochloride) (PAH) was coated onto them using the layer-by-layer deposition method such that a subsequent base-catalyzed silanization could readily form a 60 nm thick silica shell around the PAN layer by a biomimetic process. The cross linked silica shells effectively prevented the SERS-marker molecules from being liberated from the surface of the Fe3O4@Ag particles. Although the gram magnetization decreased nearly to one-half, of the initial value because of coating with silver and silica, the remaining magnetization was nonetheless strong enough for the silica coated Fe3O4@Ag particles to be used as barcode materials operating via SERS.