The use of magnetic force microscopy (MFM) to detect probe-sample interactions from superparamagnetic nanoparticles in vitro in ambient atmospheric conditions is reported here. By using both magnetic and nonmagnetic probes in dynamic lift-mode imaging and by controlling the direction and magnitude of the external magnetic field applied to the samples, it is possible to detect and identify the presence of superparamagnetic nanoparticles. The experimental results shown here are in agreement with the estimated sensitivity of the MFM technique. The potential and challenges for localizing nanoscale magnetic domains in biological samples is discussed.

In the present work we provide magnetic force microscopy (MFM) analysis on particles of a paramagnetic spin‐probe lithium octa‐n‐butoxy‐naphthalo‐cyanine (LiNc‐BuO) used for EPR oximetry. We demonstrate how MFM can generate a magnetic contrast in ambient air for LiNc‐BuO particles when they assemble into structures >50 nm in size. The same sample when assembled into particles <10 nm in size failed to show contrast in MFM images. The potential for utilizing MFM to understand the magnetic signature of paramagnetic nanoparticles in biological samples is discussed.