Measurement of Viscosity of Cellular Mediums Using Brownian Motion

Abstract

The viscosity of an artificial biological medium developed in Vincent Noireaux’s laboratory based on cytoplasm extracted from cells will be determined. These measurements will allow for comparison of the viscosity of the artificial medium used for in vitro protein expression with that of real cytoplasm used in cells. Using an optical microscope, the displacement after thirty seconds time interval of a one micrometer latex bead in the medium. The displacement measurements form a distribution. The root mean square of the displacement is the square root of 2Dt, where D is the diffusion coefficient and t is the time. From the diffusion coefficient, using the Stokes-Einstein equation, D = KbT/(6*pi*nu*a), where Kb is Boltzmann's constant, a is the radius of the bead, and nu gives the viscosity of the medium. The viscosity of water will be determined as a baseline and validation of the procedure, before measuring the viscosity of the medium.