Interrogation of Bilayers in a Multi-Droplet Cluster for Membrane-Based Sensing

The long-term vision of our work is to create a new class of smart material that utilizes networks of active, synthetic cell membranes for sensing, actuation, and energy harvesting. Having multiple membrane structures is specifically targeted because a higher density of functional membranes is expected to enable amplification and collective utility, similar to how living tissues and organisms utilize networks of highly connected cells to accomplish large tasks. While there are several known methods for assembling droplet-based networks of synthetic lipid bilayers, there has been much less effort to develop methods for electrically characterizing each interface in a multi-bilayer-droplet network. This paper specifically focuses on a strategy for using electrical measurements to independently record transmembrane currents occurring at each bilayer in multi-bilayer networks where the number of bilayers present is equal to or greater than the number of droplets in the system. Using a multichannel patch clamp amplifier, we develop a measurement technique for sequentially assigning sensing electrodes to apply a non-zero voltage or function as virtual ground (V=0). Experimental studies on a three-droplet cluster containing three bilayers confirm the validity of the proposed approach for independently interrogating each membrane, and the results allow extension of the method to networks with 4–7 droplets. Furthermore, alamethicin peptide gating is monitored using the measurement cycle in order to interrogate all interfaces. Due to high total membrane area, highly packed systems can provide an increase in the magnitude of sensing current generated by a stimulus. Such amplification could feasibly be employed in droplet-based hair cell sensing applications in which airflow or vibration acts as the perturbation source, and the proposed approach and challenges for interrogating the transduction response in a multi-membrane hair cell sensor are discussed herein.