The present invention describes methods for preparing high quality nanoparticles, i.e., metal oxide based nanoparticles of uniform size and monodispersity. The nanoparticles advantageously comprise organic alkyl chain capping groups and are stable in air and in nonpolar solvents. The methods of the invention provide a simple and reproducible procedure for forming transition metal oxide nanocrystals, with yields over 80%. The highly crystalline and monodisperse nanocrystals are obtained directly without further size selection; particle size can be easily and fractionally increased by the methods. The resulting nanoparticles can exhibit magnetic and/or optical properties. These properties result from the methods used to prepare them. Also advantageously, the nanoparticles of this invention are well suited for use in a variety of industrial applications, including cosmetic and pharmaceutical formulations and compositions.
 The United States Government may have certain rights in the present invention pursuant to partial funding by grants from the Materials Research Science and Engineering Center (DMR-0213574 MRSEC) and the Nanoscale Science and Engineering Center (CHE-0117752 NSEC) of the National Science Foundation and pursuant to partial funding by the U.S. Department of Energy, Office of Basic Energy Sciences, through the Catalysis Futures grant DE-FG02-03ER15463, and in part by the (i) the MRSEC program of the National Science Foundation under award number DMR-0213574, and NSF-CAREER award, DMR-0348938.