Frequency-Modulated Wave Dielectrophoresis of Vesicles And Cells: Periodic U-Turns at the Crossover Frequency

Abstract

We have formulated the dielectrophoretic force exerted on micro/nanoparticles upon the application of frequency-modulated (FM) electric fields. By adjusting the frequency range of an FM wave to cover the crossover frequency fX in the real part of the Clausius-Mossotti factor, our theory predicts the reversal of the dielectrophoretic force each time the instantaneous frequency periodically traverses fX. In fact, we observed periodic U-turns of vesicles, leukemia cells, and red blood cells that undergo FM wave dielectrophoresis (FM-DEP). It is also suggested by our theory that the video tracking of the U-turns due to FM-DEP is available for the agile and accurate measurement of fX. The FM-DEP method requires a short duration, less than 30 s, while applying the FM wave to observe several U-turns, and the agility in measuring fX is of much use for not only salty cell suspensions but also nanoparticles because the electric-field-induced solvent flow is suppressed as much as possible. The accuracy of fX has been verified using two types of experiment. First, we measured the attractive force exerted on a single vesicle experiencing alternating-current dielectrophoresis (AC-DEP) at various frequencies of sinusoidal electric fields. The frequency dependence of the dielectrophoretic force yields fX as a characteristic frequency at which the force vanishes. Comparing the AC-DEP result of fX with that obtained from the FM-DEP method, both results of fX were found to coincide with each other. Second, we investigated the conductivity dependencies of fX for three kinds of cell by changing the surrounding electrolytes. From the experimental results, we evaluated simultaneously both of the cytoplasmic conductivities and the membrane capacitances using an elaborate theory on the single-shell model of biological cells. While the cytoplasmic conductivities, similar for these cells, were slightly lower than the range of previous reports, the membrane capacitances obtained were in good agreement with those previously reported in the literature.Electronic supplementary materialThe online version of this article (10.1186/s11671-018-2583-5) contains supplementary material, which is available to authorized users.

Dielectric characterization of Babesia bovis using the dielectrophoretic crossover frequency

“…Normalization is crucial in data processing, especially in biological samples, to account for the sample-to-sample variation observed [60]. In a similar study, Weng et al normalized the crossover frequencies as a function of particle diameter to facilitate the comparison of trends [61] and previously published experimental results [39,[62][63][64].…”

“…In a similar study, Weng et al. normalized the crossover frequencies as a function of particle diameter to facilitate the comparison of trends [61] and previously published experimental results [39, 62–64]. To eliminate the impact of the measurement scale, we normalized the infected cells’ data using min–max normalization.…”

Methods of Generating Dielectrophoretic Force for Microfluidic Manipulation of Bioparticles

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Dielectrophoresis: From Molecular to Micrometer-Scale Analytes

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