  An effective approach to isolation of sub-micro sized particles is desired to
separate cancer and healthy cells or in therapy of Parkinson's and Alzheimer's
disease. However, since bioparticles span a large size range comprising several
orders of magnitude, development of an adequate separation method is a
challenging task. We consider a collection of non-interacting Brownian
particles of various sizes moving in a symmetric periodic potential and
subjected to an external unbiased harmonic driving as well as a constant bias.
We reveal a nonintuitive, yet efficient, separation mechanism based on thermal
fluctuations induced negative mobility phenomenon in which particles of a given
size move in a direction opposite to the applied bias. By changing solely
temperature of the system one can separate particles of various strictly
defined sizes. This novel approach may be important step towards development of
point-of-care lab-on-a-chip devices.
