Determination of electrophysiological properties of human monocytes and THP-1 cells by dielectrophoresis

Abstract

Introduction: Dielectrophoresis (DEP) is based on polarization and bioparticle movement in applied electric fields. Each type of cells has its own electrical properties within the DEP spectra and undergoes significant changes in direction of frequency following an increase of an applied nonuniform alternating current (AC) electric field. Therefore, DEP can be an effective technique for characterization and separation of different cells. The goal of the current study was to determine the electrophysiological properties of human monocytes and a human monocytic cell line originated from an acute monocytic leukemia patient (THP-1), using a lab on a chip (LOC) device that utilised microarray dot electrodes.
 Methods: Ten microliters of human monocytes isolated from peripheral blood mononuclear cells and highly confluent THP-1 cells were diluted in DEP medium and added to the spacer of the LOC device. Subsequently, the AC signal in the range of 10 kHz to 2 MHz was supplied to the LOC device, and the dynamic behaviours of monocytes and THP-1 cells due to the DEP force were observed. Images were captured and analyzed using MATLAB software.
 Results: Microscopic visualization showed that THP-1 cells were physically larger than human monocytes. The dielectric parameters (radius, diameter, and conductivity and permittivity of the cytoplasm and membrane) were greater for THP-1 cells compared to monocytes. The cross-over frequencies for THP-1 cells and monocytes were respectively 66 kHz and 280 kHz.
 Conclusion: In conclusion, the DEP spectra reflected the morphological differences between monocytes and THP-1 cells. The dielectric properties for each type of cells can be used as the criteria in the development of DEP-based characterization assays.

Dielectrophoretic characterization of macrophage phenotypes

“…Another study compared THP‐1 cell line monocytes and primary peripheral blood monocytes at a medium conductivity of 100 µS/cm. They found that the crossover frequencies were very different from each other: 66 and 280 kHz, respectively [30]. Another DEP characterization study of THP‐1 cells conducted in medium with conductivity of 104 µS/cm reported a crossover frequency (18.7 kHz) very close to our measurement [33].…”

“…Our results show that monocytes and mature macrophages differ in DEP properties are in general agreement with the literature. Monocyte-U937 150 20 [50] Monocyte-THP-1 Monocyte-from human blood 66 280 100 [30] Monocyte-THP-1 18.7 104 [33] used in our experiments, the crossover frequency of THP-1 monocytes was much higher than macrophage phenotypes. In contrast, the previous DEP characterization of U937-derived monocytes and macrophages at medium conductivity of 20 µS/cm by Elitas et al showed that monocytes have a lower crossover frequency (17 kHz) than macrophages (30 kHz) [31].…”

“…However, the DEP properties of macrophages are poorly understood. One study investigated the electrophysiological properties of primary human monocytes and the human THP-1 monocytic cell line via DEP and showed that dielectric properties differed between monocytes from the two sources [30]. In another study where human monocytes and nonactivated macrophages (M0) were compared, monocytes and macrophages exhibited different crossover frequencies (the frequency at which cell behavior transitions from pDEP to nDEP or vice versa) and were, therefore, separable by DEP [31].…”

Dielectrophoretic and Electrical Impedance Differentiation of Cancerous Cells Based on Biophysical Phenotype

“…According to the literature, these different DEP frequency responses of cancer and normal blood cells may be explained and expressed by Gascoyne and Shim [7] in terms of reciprocal cell "dielectric phenotype" 1/𝑅𝜙, where 𝜙 represents the membrane folding factor (the ratio of actual membrane area to that of the idealized smooth shell) and R is the cell radius. Many studies have reported that cancer cells have a larger folding factor and radii than both blood cells and normal cells of comparable origin [4,5,8,[30][31][32][33][34]. A plausible explanation could be related to an increase in the membrane cholesterol or the membrane lipid rafts in cancer cells [35,36].…”

Dielectrophoretic Manipulation of Cancer Cells and Their Electrical Characterization

“…With respect to sorting and identification of various target cells, different external stimuli have been employed as an electric field in the case of electrophoresis − and dielectrophoresis, a magnetic field for magnetophoresis, , a beam of light for photophoresis, , and a temperature gradient in the case of thermophoresis. − Among most well-known noninvasive manipulation methods at the micro and nanoscale level, dielectrophoresis (DEP) was recognized as one of the methods with great applicability potential at the level of bioparticles such as DNA, − RNA, proteins, − bacteria − or viruses, − blood cells, − rare cells including circulating tumor cells (CTCs), − and stem cells, − while behavior of electrical properties may be realized based on the evolution of electrical impedance determined with broadband dielectric spectroscopy (BDS). , Cancer cells characterization were not neglected by these type of studies, and a lot of cancerous cells starting from lung ,, to cervical ,, were involved in studies regarding evaluation of the electrical properties.…”