Microcavity in-line Mach-Zehnder interferometer and electrochemical assays combined for cell monitoring system

Abstract

Nowadays, multi-domain systems are crucial for accurate measurements since they improve error avoidance in empirical observations by supplementing one domain with the other. Such an approach also yields more useful information about the sample under study. In this work, we present the results obtained from a sensing system composed of a microcavity inline Mach-Zehnder interferometer (μIMZI) combined with indium tin oxide (ITO) electrodes, which is the first approach to two-domain, real-time, and label-free observation of cell behavior. The µIMZI structure was manufactured with a femtosecond laser ablation process in the side surface of single-mode optical fiber. It is susceptible to refractive index (RI) change within its volume, i.e., hundreds of picolitres. The μIMZI sensitivity to RI reaches over 15,000 nm/RIU. The μIMZI was attached to the glass plate with eight ITO electrodes formed using laser irradiation. This optical and electrochemical domain system was used for cell medium measurements, followed by one hour of HepG2 cells monitoring. Finally, trypsin was added to the solution, and its effects on the HepG2 cells were investigated optically and electrochemically. The presented monitoring setup and obtained results are proof of concept for a multi-domain cell monitoring system.