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Entropy 2014, 16(8), 4322-4337; doi:10.3390/e16084322

Exclusion-Zone Dynamics Explored with Microfluidics and Optical Tweezers

1
Department of Biophysics and Radiation Biology, Semmelweis University, Tűzoltó utca 37-47, Budapest H1094, Hungary
2
Faculty of Information Technology and Bionics, Pázmány Péter University, Práter utca 50/A, Budapest H1083, Hungary
3
MTA-SE Molecular Biophysics Research Group, Semmelweis University, Tűzoltó utca 37-47, Budapest H1094, Hungary
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 27 June 2014 / Revised: 29 July 2014 / Accepted: 29 July 2014 / Published: 4 August 2014
(This article belongs to the Special Issue Entropy and EZ-Water)
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Abstract

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. View Full-Text
Keywords: exclusion zone; microfluidic device; optical trapping; atomic force microscopy; non-equilibrium process; chemical gradient; diffusion; coupled transport exclusion zone; microfluidic device; optical trapping; atomic force microscopy; non-equilibrium process; chemical gradient; diffusion; coupled transport
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This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Huszár, I.N.; Mártonfalvi, Z.; Laki, A.J.; Iván, K.; Kellermayer, M. Exclusion-Zone Dynamics Explored with Microfluidics and Optical Tweezers. Entropy 2014, 16, 4322-4337.

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