  In-situ characterization of minute amounts of complex fluids is a challenge.
Magnetic Rotational Spectroscopy (MRS) with submicron probes offers flexibility
and accuracy providing desired spatial and temporal resolution in
characterization of nanoliter droplets and thin films when other methods fall
short. MRS analyzes distinct features of the in-plane rotation of a magnetic
probe, when its magnetic moment makes full revolution following an external
rotating magnetic field. The probe demonstrates a distinguishable movement
which changes from rotation to tumbling to trembling as the frequency of
rotation of the driving magnetic field changes. In practice, MRS has been used
in analysis of gelation of thin polymer films, ceramic precursors, and
nanoliter droplets of insect biofluids. MRS is a young field, but it has many
potential applications requiring rheological characterization of scarcely
available, chemically reacting complex fluids.
