An endothelial cell compatible biosensor fabricated using optically thin indium tin oxide silicon nitride electrodes

This study describes the fabrication and performance of an endothelial cell compatible, optically thin, indium tin oxide (ITO) microimpedance biosensor. The biosensor was constructed by sputtering a thin insulating layer of silicon nitride (Si3N4) onto a 100 nm thick ITO layer. Indium tin oxide electrodes were formed by chemically etching 250 or 500 μm diameter holes through the Si3N4 insulating layer. The exposed ITO electrode was electrically connected to an ITO counter electrode, approximately 2 cm2 in area, via a 400 μL well containing cell culture media. A lock-in amplifier circuit monitored the impedance of porcine pulmonary artery endothelial cells (PPAECs) cultivated on the electrodes as a function of frequency, between 10 and 100 kHz, and as a function of time, at 5.62 kHz. The ITO–Si3N4 microelectrodes provided consistent and repeatable impedance measurements to the attachment and spreading of PPAECs. In addition, the ITO–Si3N4 electrodes were recyclable, robust, resistant to ethanol sterilization, and had a high optical transmittance. Most importantly, the ITO–Si3N4 electrodes allowed optical access for dynamic cellular attachment imaging. The 5.62 kHz time dependent cellular impedance response to the drug Cytochalasin D further demonstrated the feasibility of using this electrode configuration for dynamic cellular impedance studies.