Membrane permeability assays play an important role in assessing drug transport activities across biological
membranes. However, in conventional parallel artificial membrane permeability assays (PAMPA), the
membrane model used is dissimilar to biological membranes physically and chemically. Here, we describe a
microfluidic passive permeability assay using droplet interface bilayers (DIBs). In a microfluidic network,
nanoliter-sized donor and acceptor aqueous droplets are alternately formed in cross-flowing oil containing
phospholipids. Subsequently, selective removal of oil through hydrophobic pseudo-porous sidewalls
induces the contact of the lipid monolayers, creating arrayed planar DIBs between the donor and acceptor
droplets. Permeation of fluorescein from the donor to the acceptor droplets was fluorometrically
measured. From the measured data and a simple diffusion model we calculated the effective permeabilities
of 5.1 106 cm s1, 60.0 106 cm s1, and 87.6 106 cm s1 with donor droplets at pH values of 7.5,
6.4 and 5.4, respectively. The intrinsic permeabilities of specific monoanionic and neutral fluorescein species
were obtained similarly. We also measured the permeation of caffeine in 10 min using UV
microspectroscopy, obtaining a permeability of 20.8 106 cm s1. With the small solution volumes, short
measurement time, and ability to measure a wide range of compounds, this device has considerable
potential as a platform for high-throughput drug permeability assays.
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