"Rheological microscopy: Local mechanical properties from microrheology"
D. T. Chen et al., Phys. Rev. Lett. 90 108301 (2003).

We demonstrate how tracer microrheology methods can be extended to study sub-micron scale variations in the viscoelastic response of soft materials; in particular, a semi-dilute solution of lambda-DNA. The polymer concentration is depleted near the surfaces of the tracer particles, within a distance comparable to the polymer correlation length. The rheology of this microscopic layer alters the tracers' motion and can be precisely quantified using one- and two-point microrheology. Interestingly, we found this mechanically distinct layer to be twice as thick as the layer of depleted concentration, likely due to solvent drainage through the locally perturbed polymer structure.