Crowding-induced anisotropic transport modulates reaction kinetics in nanoscale porous media

R Grima, S N Yaliraki, M Barahona

Research output: Contribution to journalArticlepeer-review


We quantify the emergence of persistent anisotropy in the diffusion of spherical tracer particles through a nanoscale porous medium composed of a uniform distribution of purely symmetric crowding particles. We focus on the interior of a biological cell as an example of such a medium and find that diffusion is highly directional for distances comparable to the size of some organelles. We use a geometrical procedure that avoids the standard orientational averaging to quantify the anisotropy of diffusive paths and show that the point source distributions are predominantly of prolate ellipsoidal shape as a result of local volume exclusion. This geometrical symmetry breaking strongly skews the distribution of kinetic rates of diffusion-limited reactions toward small values, leading to the result that, for short to intermediate times, almost 80% of the rates measured in an ensemble of heterogeneous media are smaller than the expected rate in an ideal homogeneous medium of similar excluded volume fraction. This crowding-induced modulation may have implications for our understanding and measurement of diffusion-controlled intracellular reaction kinetics and for experimental nanotechnology applications, such as nanoparticle-based bioimaging and drug delivery, where diffusion plays an important role.
Original languageEnglish
Pages (from-to)5380-5
Number of pages6
JournalJournal of Physical Chemistry B (Soft Condensed Matter and Biophysical Chemistry)
Issue number16
Early online date6 Apr 2010
Publication statusPublished - 29 Apr 2010


  • Diffusion
  • Nanoparticles
  • Magnetic properties
  • Mathematical methods


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