Tunable Mass Separation via Negative Mobility

Abstract

A prerequisite for isolating diseased cells requires a mechanism for effective mass-based separation. This objective, however, is generally rather challenging because typically no valid correlation exists between the size of the particles and their mass value. We consider an inertial Brownian particle moving in a symmetric periodic potential and subjected to an externally applied unbiased harmonic driving in combination with a constant applied bias. In doing so we identify a most efficient separation scheme which is based on the anomalous transport feature of negative mobility, meaning that the immersed particles move in the direction opposite to the acting bias. This work is first of its kind in demonstrating a tunable separation mechanism in which the particle mass targeted for isolation is effectively controlled over a regime of nearly two orders of mass-magnitude upon changing solely the frequency of the external harmonic driving. This approach may provide mass selectivity required in present and future separation of a diversity of nano and micro-sized particles of either biological or synthetic origin.

Diffusion in a biased washboard potential revisited

“…We have taken into account the above constraints and constructed the phase diagram of occurrence of the nonmonotonic temperature dependence of diffusion in the system described by the Langevin equation (5). This is an essentialy new result which has not been presented in the literature.…”

“…The dimensionless thermal noise ζ(t) assumes the same statistical properties as ξ(t), namely, it is a Gaussian stochastic process with vanishing mean ζ(t) = 0 and the correlation function ζ(t)ζ(ŝ) = δ(t −ŝ). From now on we will use only the dimensionless variables and shall omit the hat in all quantities appearing in the Langevin equation (5).…”

“…In this study we use extensive numerical simulations of the underdamped Langevin dynamics (5) to construct a phase diagram for occurrence of the non-monotonic temperature dependence of diffusion. In doing so we determine all values of the friction coefficient γ as well as the bias f in the numerically accessible parameters range for which the diffusion coefficient display the abnormal dependence on temperature.…”

“…In the bistability regime, the above analysis allows to construct a two state Markov process which approximates the Langevin equation (5). Jumps between the locked and running states are driven solely by thermal fluctuations.…”

Coexistence of absolute negative mobility and anomalous diffusion

“…The phenomenon of absolute negative mobility (ANM) [6][7][8][9][10][11][12][13][14][15] may be regarded as a form of anomalous directed transport. In this case, transported particles move in a direction opposite to the net acting force around zero bias.…”