Interdigitated aluminium and titanium sensors for assessing epithelial barrier functionality by electric cell-substrate impedance spectroscopy (ECIS)

Abstract

Electric cell-substrate impedance spectroscopy (ECIS) enables non-invasive and continuous read-out of electrical parameters of living tissue. The aim of the current study was to investigate the performance of interdigitated sensors with 50 μm electrode width and 50 μm inter-electrode distance made of gold, aluminium, and titanium for monitoring the barrier properties of epithelial cells in tissue culture. At first, the measurement performance of the photolithographic fabricated sensors was characterized by defined reference electrolytes. The sensors were used to monitor the electrical properties of two adherent epithelial barrier tissue models: renal proximal tubular LLC-PK1 cells, representing a normal functional transporting epithelium, and human cervical cancerderived HeLa cells, forming non-transporting cancerous epithelial tissue. Then, the impedance spectra obtained were analysed by numerically fitting the parameters of the two different models to the measured impedance spectrum. Aluminium sensors proved to be as sensitive and consistent in repeated online-recordings for continuous cell growth and differentiation monitoring as sensors made of gold, the standard electrode material. Titanium electrodes exhibited an elevated intrinsic ohmic resistance in comparison to gold reflecting its lower electric conductivity. Analysis of impedance spectra through applying models and numerical data fitting enabled the detailed investigation of the development and properties of a functional transporting epithelial tissue using either gold or aluminium sensors. The result of the data obtained, supports the consideration of aluminium and titanium sensor materials as potential alternatives to gold sensors for advanced application of ECIS spectroscopy.

Bridging barriers: advances and challenges in modeling biological barriers and measuring barrier integrity in organ-on-chip systems

“…Schmiedinger et al compared electrodes fabricated using various metals, finding that aluminum electrodes had similar impedance outputs across frequencies compared to gold, while titanium had higher impedance values, likely because of higher inherent resistance within the material. 269 A similar trend was observed by Walter et al in a head-to-head comparison of ITO and thin layer gold electrodes, where the gold electrodes were ultimately chosen for subsequent experiments due to their higher conductivity. 219 The method of depositing metal onto a substrate also plays a key role in the inherent resistivity of electrodes and electrical traces.…”

Porous Membrane Electrical Cell–Substrate Impedance Spectroscopy for Versatile Assessment of Biological Barriers In Vitro

“…Notably, the variances for sputtered vs gold leaf electrode resistivity are comparable, indicating that the lab-based gold leaf fabrication is as reproducible as commercial-grade sputtering. Given the context of PM-ECIS as a platform for measuring biological barriers, this statistical analysis of our microfabrication process provides relevant insight into the interpretation of data obtained from our biological experiments and is also aligned with similar empirical approaches in other publications. − …”