Positional control of superparamagnetic iron oxide nanoparticles in silica beads

The synthesis of supermagnetic iron oxide nanoparticles containing silica beads (up to 40% (w/w)) was investigated using water-in-oil microemulsion technique. Supermagnetic iron oxide nanoparticles (SPIONs) were prepared by alkaline co-precipitation of ferric and ferrous chloride in aqueous solution. Iron oxide dispersions coated with either citric acid or PVA were added to a 0.002 M solution of sodium-bis(2-ethylhexyl)sulfosuccinate in octane. The coated particles were emulsified by sonification into the continuous phase for half an hour. 15 μl of pre-hydrolyzed TMOS (TMOS:MeOH:H2O=1:22:6), 2mM M HCl, and N(CH3)4OH were added and the mixture was sonificated to allow reaction in the absence of ultrasound. It was observed that crosslinking between the PVA and TMOS occurred by the polycondensation reaction. Result shows that assembly of nanoparticles in silica/nanoparticle composite beads can be controlled by their surface coating.