Exclusion-zone dynamics explored with microfluidics and optical tweezers

István N. Huszár, Zsolt Mártonfalvi, András József Laki, Kristóf Iván, Miklós Kellermayer

Research output: Contribution to journalArticle

8 Citations (Scopus)


The exclusion zone (EZ) is a boundary region devoid of macromolecules and microscopic particles formed spontaneously in the vicinity of hydrophilic surfaces. The exact mechanisms behind this remarkable phenomenon are still not fully understood and are debated. We measured the short- and long-time-scale kinetics of EZ formation around a Nafion gel embedded in specially designed microfluidic devices. The time-dependent kinetics of EZ formation follow a power law with an exponent of 0.6 that is strikingly close to the value of 0.5 expected for a diffusion-driven process. By using optical tweezers we show that exclusion forces, which are estimated to fall in the sub-pN regime, persist within the fully-developed EZ, suggesting that EZ formation is not a quasi-static but rather an irreversible process. Accordingly, the EZ-forming capacity of the Nafion gel could be exhausted with time, on a scale of hours in the presence of 1 mM Na2HPO4. EZ formation may thus be a non-equilibrium thermodynamic cross-effect coupled to a diffusion-driven transport process. Such phenomena might be particularly important in the living cell by providing mechanical cues within the complex cytoplasmic environment.

Original languageEnglish
Pages (from-to)4322-4337
Number of pages16
Issue number8
Publication statusPublished - Aug 2014


  • Atomic force microscopy
  • Chemical gradient
  • Coupled transport
  • Diffusion
  • Exclusion zone
  • Microfluidic device
  • Non-equilibrium process
  • Optical trapping

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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