Abstract
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 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.
Highlights
Dielectrophoresis (DEP) studies of biological particles have progressed from the microscopic scale of cells and bacteria, through the much smaller scale of virions to the molecular scale of DNA and proteins [1]
At least 22 different globular proteins have been investigated for their DEP responses [3,4,5,6,7]
In this paper we examine aspects of the reported protein DEP work not covered in previous reviews, and conclude that the reported DEP responses for a range of proteins are largely consistent
Summary
Dielectrophoresis (DEP) studies of biological particles have progressed from the microscopic scale of cells and bacteria, through the much smaller scale of virions to the molecular scale of DNA and proteins [1]. A new theory is evolving in terms of a description at the molecular level of how a macroscopic dielectric sample responds to an applied electric field [8,9,10] This involves a consideration of the actual ‘cavity field’ experienced by the protein molecule, as well as the time-dependent correlation of the total electric moment of the protein. Boundary conditions assume that the electric potential, current density and displacement flux are continuous across an infinitesimally thin surface at the sphere’s interface with the surrounding medium Fine details such as those that occur, for example, at the molecular interface between a protein and its hydration sheath are not considered. GGlolboubulalrapr ropteriontseisntus disetdudfoierdthefirordietlhecetirropdhioerleecsitsro(DphEoPr)erseisspo(nDsEe,Pw) ithretshpeoirnhsey,drwodityhnamthiecir hy(Sdtrookdeys)nraamdiiicl(oSctaotkeeds)onratdhiei elomcaptierdicaolnretlhaetioemnsphiirpicbaeltrweleaetniopnrsohtiepinbseitzweeaenndpmrootleeicnulsaizr ewaenigdhmt (odloetctueldar wceuigrvhet)(dporottveiddecdurbvye)MparlovveirdnedPabnyalMytaiclvael®rn(ZPaentaasliyzteircaNl®a(nZoeZtaSs)i.zer Nano ZS)
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