Tunable, Metal-Loaded Polydopamine Nanoparticles Analyzed by Magnetometry

We report the preparation and study of Mn(III)-, Fe(III)-, Co(II)-, Ni(II)-, Cu(II)-, Zn(II)-, and Ga(III)-loaded polydopamine nanoparticles (PDA-NPs) via autoxidation polymerization of metal–dopamine complexes in the presence of free dopamine. An analysis of the doping range and parameters that influence final particle morphology is presented. In addition, magnetometry provides a probe of the general electronic structure and electronic interactions for Mn(III)-, Ni(II)-, and Co(II)-loaded PDA-NPs. PDA-NPs doped with Mn(III) are found to have high spin, low anisotropy, and weak magnetic coupling and are therefore predicted to have superior relaxivity behavior compared to previously studied Fe(III)-loaded PDA-NPs. Comparison of Mn(III)- and Fe(III)-loaded PDA-NP relaxivity confirms the predictive ability of the magnetometry measurements.