A coater employing near-critical carbon dioxide as the fluidizing medium and supercritical carbon dioxide as the solvent was developed for encapsulating nanoparticles. The fluidization behavior of different materials with different particle sizes was under investigation as well as the in situ characterization of the aerosol generated by the Rapid Expansion of Supercritical Solutions process. First experiments were carried out successfully to encapsulate fine aluminum particles with different waxes and trinitrotoluene, respectively.