Ferrite plating on porous silica microspheres for ultrasonic contrast agents

Porous silica microspheres, 1-3 μm in diameter, were coated with Fe₃O₄ by “reactor method” ferrite plating. The polycrystalline Fe₃O₄ coating was synthesized from an aqueous solution (pH=7.3) of FeCl₂ at 60-70°C, using oxidizing solution of NaNO₂ mixed with CH ₃COONH₄ (pH buffer). The magnetite capsulated silica microspheres can be potentially used for contrast agents for clinical ultrasonography, especially for blood flowmetry; the air trapped in the silica pores enhances the ultrasound echogenicity. The contrast agents are controllable by magnetic fields, and their virtual density can be adjusted to that of ambient fluid by changing the thickness of the Fe₃O₄ coating