Dispersion-relation Phase Spectroscopy (DPS)

Posted on March 26, 2012 by admin

We used quantitative phase imaging to measure the dispersion relation, i.e. decay rate vs. spatial mode, associated with mass transport in live cells. This approach applies equally well to both discrete and continuous mass distributions without the need for particle tracking. From the quadratic experimental curve specific to diffusion, we extracted the diffusion coefficient as the only fitting parameter. The linear portion of the dispersion relation reveals the deterministic component of the intracellular transport. Our data show a universal behavior where the intracellular transport is diffusive at small scales and deterministic at large scales. Measurements by our method and particle tracking show that, on average, the mass transport in the nucleus is slower than in the cytoplasm.


a) Quantitative phase image of 1μm polystyrene beads in glycerol. Colorbar indicates pathlength in nm. b) Mean squared displacements (MSD) obtained by tracking individual beads in a. The inset illustrates the trajectory of a single bead. c) Decay rate vs. spatial mode, G(q), associated with the beads in a. The dash ring indicates the maximum q values allowed by the resolution limit of the microscope. d) Azimuthal average of data in c) to yield G(q). The fits with the quadratic function yields the value of the diffusion coefficient as indicated.

DPS related Publications

  1. R. Wang, Z, Wang, L. Millet, M. U.Gillette, A. J. Levine, and G. Popescu, Dispersion-relation phase spectroscopy of intracellular transport, Opt. Exp., 19 (21), 2011.
  2. R. Wang, Z. Wang, J. Leigh, N. Sobh, L. Millet, M. U. Gillette, A. J. Levine and G. Popescu, One-dimensional deterministic transport in neurons measured by dispersion-relation phase spectroscopy, J. Phys. Cond. Matt., 23, 2011