Nano-encapsulated manganese oxide (NEMO) particles are
noteworthy
contrast agents for magnetic resonance imaging (MRI) due to their
bright, pH-switchable signal (“OFF” to “ON”
at low pH), high metal loading, and targeting capability for increased
specificity. For the first time, we performed a head-to-head comparison
of NEMO particles from In-house and commercialized sources (US Nano
vs Nanoshel) to assess their potential as bright T1MRI
contrast agents. Manganese oxide nanocrystals (MnO, Mn2O3, and Mn3O4) were systematically
evaluated for size, chemistry, release of manganese ions, and MRI
signal pre- and post-encapsulation within poly(lactic-co-glycolic acid) (PLGA). Suprisingly, a majority of the commercialized
formulations were not as advertised by displaying unintended sizes,
morphologies, chemistry, dissolution profiles, and/or MRI signal that
precludes in vivo use. US Nano’s Mn3O4and Mn2O3nanocrystals contained impurities
that impacted Mn ion release as well as micron-sized rodlike structures.
Nanoshel’s MnO and Mn2O3nanoparticles
had very large hydrodynamic sizes (>600 nm). In-house MnO and Nanoshel’s
Mn3O4nanoparticles demonstrated the best characteristics
with brighter T1MRI signals, small hydrodynamic sizes,
and high encapsulation efficiencies. Our findings highlight that researchers
must confirm the properties of purchased nanomaterials before utilizing
them in desired applications, as their experimental success may be
impacted.