A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media

Abstract

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with the miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10 s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system’s impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 min. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1 s. Overall, the new microfluidic device can be used for the dielectric characterization of biological cells in physiological buffers for various cell screening applications.

Changes in Electrical Capacitance of Cell Membrane Reflect Drug Partitioning-Induced Alterations in Lipid Bilayer

“…In our previous study [ 16 ], we demonstrated that dendritic gold nanostructures provide the context to measure cell properties in a physiological buffer due to the significant reduction in the EP effect. Herein, we explored the potential use of the microfluidic device for real-time monitoring of cell membrane capacitance in response to different doses of amiodarone compared to aspirin/acetylsalicylic acid and glucose.…”

“…The experimental setup is shown in Figure 1 A. The suspended PC-3 cells in RPMI-1640 were injected from the inlet to the microchannel and captured with gravitational force [ 16 ]. The syringe pump injected the growth media with a flow speed of 3 µL/min to wash uncaptured cells and nourish the cells inside the wells during the measurements.…”

“…In our most recent study, DS was applied on PC-3 cell suspension in growth media (high conductive media), which was captured in microwells with dendritic nanostructured gold surfaces. Dielectric properties of the cells were extracted to show the stability of the cells in the microfluidic system by using physiological media [ 16 ].…”

“…In our recent study, we reported a microfluidic impedance spectroscopy technique that enables the measurement of dielectric properties of biological cells in high-conductivity physiological buffers [ 16 ]. Specifically, this non-invasive technique captures individual cells on an electro-activated microwell array, which enables real-time characterization of cellular dielectric properties, such as membrane capacitance and cytoplasmic resistance.…”

Impedance-Based Neutralizing Antibody Detection Biosensor with Application in SARS-CoV-2 Infection

“…A dielectrophoretic (DEP) force is imposed on the suspended particles based on their relative polarizability with respect to the ionic fluid. 24 At a given AC frequency, more polarizable particles than the fluid are attracted to the high electric field regions near the electrodes, exhibiting positive DEP. 25 Otherwise, they are repelled from the near electrode regions (i.e., negative DEP).…”