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Open AccessArticle

Protein Dielectrophoresis: I. Status of Experiments and an Empirical Theory

1
Fraunhofer Institute for Cell Therapy and Immunology, Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, 14476 Potsdam-Golm, Germany
2
School of Engineering: Institute for Integrated Micro and Nanosystems, University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JF, UK
*
Author to whom correspondence should be addressed.
Micromachines 2020, 11(5), 533; https://doi.org/10.3390/mi11050533
Received: 3 May 2020 / Revised: 20 May 2020 / Accepted: 20 May 2020 / Published: 22 May 2020
(This article belongs to the Special Issue Micromachines for Dielectrophoresis)
The dielectrophoresis (DEP) data reported in the literature since 1994 for 22 different globular proteins is examined in detail. Apart from three cases, all of the reported protein DEP experiments employed a gradient field factor ∇Em2 that is much smaller (in some instances by many orders of magnitude) than the ~4 1021 V2/m3 required, according to current DEP theory, to overcome the dispersive forces associated with Brownian motion. This failing results from the macroscopic Clausius–Mossotti (CM) factor being restricted to the range 1.0 > CM > −0.5. Current DEP theory precludes the protein’s permanent dipole moment (rather than the induced moment) from contributing to the DEP force. Based on the magnitude of the β-dispersion exhibited by globular proteins in the frequency range 1 kHz–50 MHz, an empirically derived molecular version of CM is obtained. This factor varies greatly in magnitude from protein to protein (e.g., ~37,000 for carboxypeptidase; ~190 for phospholipase) and when incorporated into the basic expression for the DEP force brings most of the reported protein DEP above the minimum required to overcome dispersive Brownian thermal effects. We believe this empirically-derived finding validates the theories currently being advanced by Matyushov and co-workers.
Keywords: Clausius–Mossotti function; dielectrophoresis; dielectric spectroscopy; interfacial polarization; proteins Clausius–Mossotti function; dielectrophoresis; dielectric spectroscopy; interfacial polarization; proteins
MDPI and ACS Style

Hölzel, R.; Pethig, R. Protein Dielectrophoresis: I. Status of Experiments and an Empirical Theory. Micromachines 2020, 11, 533.

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