Effects of electrode diameter on the detection sensitivity and frequency characteristics of electric cell-substrate impedance sensing

Abstract

Cell-based electrochemical impedance spectroscopy (EIS) has emerged as a label-free approach to monitor whole cellular behavior in response to the environmental stimuli in real time. The measured impedance is strongly dependent on the attached cells, the sensing electrode size, and the constriction resistance between the sensing electrode and its counter electrode. However, determining the optimal electrode size for sensitive detection of impedance characteristics of the attached cells remains a challenge. In this study, four different cell lines (MDCK, MCF-7, HUVEC, and MDA-MB-231 cells) were cultured on the sensing electrodes with four different diameters, 250, 100, 50, and 25 μm, and impedance measurements were performed at frequencies ranging from 25 Hz to 64 kHz using electric cell-substrate impedance sensing (ECIS) method. As the diameter of sensing electrode decreases, the peak value (optimal detection sensitivity) of the normalized resistance spectrum decreases and the peak position (optimal detection frequency) shifts to the high-frequency region. These criteria were applied to sensitively measure impedance changes of MDA-MB-231 cells in response to TGF-β1 treatment. The transient increase of measured impedance after TGF-β1 treatment coincided with the augmented formation of the peripheral paxillin-rich sites and the increased cell migration rate, while little difference in cell spreading area was observed. Our results suggest that 250 μm is approximately the optimal electrode diameter for EIS measurement if sensitively monitoring the morphological changes of adherent cells is required.