  Superparamagnetic iron oxide nanoparticles (SPIONs), due to their
controllable sizes, relatively long in vivo half-life and limited
agglomeration, are ideal for biomedical applications such as magnetic labeling,
hyperthermia cancer treatment, targeted drug delivery and for magnetic
resonance imaging (MRI) as contrast enhancement agents. In order to understand
how SPIONs interact with cells and cellular membranes it would be of interest
to characterize individual SPIONs at the nanoscale in physiologically relevant
conditions without labeling them. We demonstrate that Magnetic Force Microscopy
(MFM) can be used to image SPIONs in air as well as in liquid. The magnetic
properties of bare and SiO2 coated SPIONs are compared using MFM. We report
that surface modification using (3-mercaptopropyl)-trimethoxysilane
significantly improves adsorption and distribution of SPIONs on gold surfaces.
To obtain proof of principle that SPIONS can be imaged with MFM inside the cell
we imaged SPIONs buried in thin polymer films (polystyrene (PS) and poly
methyl-methacrylate (PMMA)). This opens the possibility of visualizing SPIONs
inside the cell without any labeling or modifications and present MFM as a
potential magnetic analogue for fluorescence microscopy. The results of these
studies may have a valuable impact for characterization and further development
of biomedical applications of SPIONs and other magnetic nanoparticles.
