Manganese Oxide Nanoparticle Synthesis by Thermal Decomposition of Manganese(II) Acetylacetonate.

For biomedical applications, metal oxide nanoparticles such as iron oxide and manganese oxide (MnO), have been used as biosensors and contrast agents in magnetic resonance imaging (MRI). While iron oxide nanoparticles provide constant negative contrast on MRI over typical experimental timeframes, MnO generates switchable positive contrast on MRI through dissolution of MnO to Mn at low pH within cell endosomes to 'turn ON' MRI contrast. This protocol describes a one-pot synthesis of MnO nanoparticles formed by thermal decomposition of manganese(II) acetylacetonate in oleylamine and dibenzyl ether. Although running the synthesis of MnO nanoparticles is simple, the initial experimental setup can be difficult to reproduce if detailed instructions are not provided. Thus, the glassware and tubing assembly is first thoroughly described to allow other investigators to easily reproduce the setup. The synthesis method incorporates a temperature controller to achieve automated and precise manipulation of the desired temperature profile, which will impact resulting nanoparticle size and chemistry. The thermal decomposition protocol can be readily adapted to generate other metal oxide nanoparticles (e.g., iron oxide) and to include alternative organic solvents and stabilizers (e.g., oleic acid). In addition, the ratio of organic solvent to stabilizer can be changed to further impact nanoparticle properties, which is shown herein. Synthesized MnO nanoparticles are characterized for morphology, size, bulk composition, and surface composition through transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy, respectively. The MnO nanoparticles synthesized by this method will be hydrophobic and must be further manipulated through ligand exchange, polymeric encapsulation, or lipid capping to incorporate hydrophilic groups for interaction with biological fluids and tissues.