A method of preparing uniform microparticles, the method comprising the steps of: (a) providing starting nanoparticles having either a hydrophobic surface or a hydrophilic surface, wherein said starting nanoparticles have a particle diameter of between 1 and 100 nm, wherein the starting nanoparticles comprise one or more magnetic materials; (b) suspending said starting nanoparticles in a first fluid phase to provide a suspension of the starting nanoparticles in said first fluid phase, wherein said first fluid phase comprises a hydrophobic solvent if the starting nanoparticles are hydrophobic, and wherein said first fluid phase comprises a hydrophilic solvent if the starting nanoparticles are hydrophilic; (c) mixing the suspension formed in step (b) with a second fluid phase in which the first fluid phase is not miscible, thereby producing an emulsion of droplets of the suspension formed in step (b) dispersed in the second fluid phase, wherein said second fluid phase comprises an aqueous phase if the first fluid phase comprises hydrophobic starting nanoparticles suspended in a hydrophobic solvent, and wherein said second fluid phase comprises a hydrophobic phase if the first fluid phase comprises hydrophilic starting nanoparticles suspended in a hydrophilic solvent; (d) evaporating enough of the hydrophobic or hydrophilic solvent from the emulsion to self-assemble nanoparticles to form microparticles suspended now in the second fluid phase; (e) providing a polymerizable monomer to the second fluid phase; and (f) polymerizing the polymerizable monomer to provide a polymer layer on the microparticles; wherein the coated microparticles have a magnetic core that comprises in excess of 50% of the particle's mass, wherein the magnetic core is the bare nanoparticle without their hydrophobic or hydrophilic coatings and without a polymer coating; and wherein the size of the coated microparticles ranges from 0.01 to 10 μm. (a) providing starting nanoparticles having either a hydrophobic surface or a hydrophilic surface, wherein said starting nanoparticles have a particle diameter of between 1 and 100 nm, wherein the starting nanoparticles comprise one or more magnetic materials; (b) suspending said starting nanoparticles in a first fluid phase to provide a suspension of the starting nanoparticles in said first fluid phase, wherein said first fluid phase comprises a hydrophobic solvent if the starting nanoparticles are hydrophobic, and wherein said first fluid phase comprises a hydrophilic solvent if the starting nanoparticles are hydrophilic; (c) mixing the suspension formed in step (b) with a second fluid phase in which the first fluid phase is not miscible, thereby producing an emulsion of droplets of the suspension formed in step (b) dispersed in the second fluid phase, wherein said second fluid phase comprises an aqueous phase if the first fluid phase comprises hydrophobic starting nanoparticles suspended in a hydrophobic solvent, and wherein said second fluid phase comprises a hydrophobic phase if the first fluid phase comprises hydrophilic starting nanoparticles suspended in a hydrophilic solvent; (d) evaporating enough of the hydrophobic or hydrophilic solvent from the emulsion to self-assemble nanoparticles to form microparticles suspended now in the second fluid phase; (e) providing a polymerizable monomer to the second fluid phase; and (f) polymerizing the polymerizable monomer to provide a polymer layer on the microparticles;