Passive and parallel microfluidic formation of droplet interface bilayers (DIBs) for measurement of leakage of small molecules through artificial phospholipid membranes

We present a passive microfluidic system for easy and rapid generation of Droplet Interface Bilayer pairs, each formed with two aqueous nanoliter droplets comprising controlled chemical composition. The system allows for rapid screening to quantify leakage of small molecules through artificial phospholipid bilayers. The droplets are generated, diluted and stored in-situ on the microfluidic chip. Our device comprises microfluidic Meter&Store (M&S) modules - hydrodynamic traps, which enable hard-wired operations on small - ca. 9 nL in volume - aqueous droplets including splitting, merging and derailing the droplets to side storage wells. Consequently, the droplets are locked and positioned next to each other and form bilayers at the point of contact between the nanoliter aqueous compartments. Additionally, a set of trap modules provides the possibility for in situ preparation of dilutions of a sample. We demonstrated the basic capacity of the trap-based system for formation of an array of 12 (controllably different) lipid bilayers in less than 5 min. Thanks to the small volumes of the droplets, the system is capable for monitoring the transport across the artificial membrane within a relatively short interval - opening the possibility to use dyes and alleviating the difficulty of parallel electrophysiological measurements. We use this functionality to prepare on-chip dilutions of small molecules and determine their permeation rates through the bilayer. Finally, we used the M&S system and calcium sensitive dyes to quantify the ion flux through the model alpha-hemolysin (alpha HL) nanopores.