Variable Membrane Dielectric Polarization Characteristic in Individual Live Cells

Abstract

Investigation of the dielectric properties of cell membranes plays an important role in understanding the biological activities that sustain cellular life and realize cellular functionalities. Herein, the variable dielectric polarization characteristics of cell membranes are reported. In controlling the dielectric polarization of a cell using dielectrophoresis force spectroscopy, different cellular crossover frequencies were observed by modulating both the direction and sweep rate of the frequency. The crossover frequencies were used for the extraction of the variable capacitance, which is involved in the dielectric polarization across the cell membranes. In addition, this variable phenomenon was investigated by examining cells whose membranes were cholesterol-depleted with methyl-β-cyclodextrin, which verified a strong correlation between the variable dielectric polarization characteristics and membrane composition changes. This study presented the dielectric polarization properties in live cells’ membranes that can be modified by the regulation of external stimuli and provided a powerful platform to explore cellular membrane dielectric polarization.

Droplet Microfluidics with MALDI-MS Detection: The Effects of Oil Phases in GABA Analysis

“…To analyze the water and oil evaporation rates, fluorescein was added into a series of 65 pL aCSF droplets to clearly visualize changes in droplet morphology and formation of the dried droplet deposit ( Figure 1 B). Particle tracking analysis 44 revealed two stages of size reduction in the deposited droplets, pinning and depinning, 47 characterized by constant contact area and constant contact angle, respectively ( Figure 1 C). During this process, the aqueous droplet held its position on the ITO surface, revealing minor in-plane motion ( Figure S2 ).…”

“…All time-lapsed images of the evaporation process were recorded using 10× and 20× objective lenses and cameras with 20 frames/s capture rates. Each droplet evaporation area was analyzed using the time-lapsed images and an in-house code, 44 created using MATLAB (Mathworks, Natick, MA) and based on a particle tracking algorithm.…”

“…The in-house MATLAB code 44 was used to analyze the area changes and particle trajectories of each droplet and surrounding oil phase during evaporation. First, the two regions of interest corresponding to the oil and droplet phases were manually selected for separate analysis.…”

On-Chip Single-Cell Bioelectrical Analysis for Identification of Cell Electrical Phenotyping in Response to Sequential Electric Signal Modulation

“…The chip electrode used was designed to generate a partial divergence array of the square gradient of the electric field vector, which can isolate randomly distributed cells by dielectrophoretic (DEP) force. This chip was fabricated through sequential photolithography, chromium lift-off, and wet etching (see Supplementary Materials Method S1 and our previous reports [ 20 ] for further detail). Before the dielectrophoresis experiment, we cleaned the chip using solvent solution (20 min in each acetone and methanol solution), piranha solution (25 min in a solution of sulfuric acid and hydrogen peroxide (H 2 SO 4 :H 2 O 2 = 3:1)), and deionized water.…”

“…These techniques evaluate an interfacial polarization of which the degree is determined depending on an AC signal applied to the cell membrane that allows intrinsic membrane dielectric properties to be extracted. The membrane dielectric properties examined with these techniques can be used as electrical phenotyping to identify cell geometrical and/or physiological alterations (e.g., cell volume, membrane integrity, constitutive elements of the membrane, and ion channel activation [ 1 , 18 , 19 , 20 , 21 , 22 , 23 ]) in response to environmental stresses.…”