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Bilayer lipid membranes (BLMs) have been studied extensively due to functional and structural similarities
to cell membranes, fostering research to understand ion-channel protein functions, measure bilayer mechanical
properties, and identify self-assembly mechanisms. BLMs have traditionally been formed across single pores in
substrates such as PTFE (Teflon). The incorporation of ion-channel proteins into the lipid bilayer enables the
selective transfer of ions and fluid through the BLM. Processes of this nature have led to the measurement of
ion current flowing across the lipid membrane and have been used to develop sensors that signal the presence of
a particular reactant (glucose, urea, penicillin), improve drug recognition in cells, and develop materials capable
of creating chemical energy from light. Recent research at Virginia Tech has shown that the incorporation of
proton transporters in a supported BLM formed across an array of pores can convert chemical energy available
in the adenosine triphosphate (ATP) into electricity. Experimental results from this work show that the
system-named Biocell-is capable of developing 2µW/cm2 of membrane area with 15μl of ATPase. Efforts to increase
the power output and conversion efficiency of this process while moving toward a packaged device present a
unique engineering problem. The bilayer, as host to the active proton transporters, must therefore be formed
evenly across a porous substrate, remain stable and yet fluid-like for protein interaction, and exhibit a large seal
resistance. This article presents the ongoing work to characterize the Biocell using impedance analysis. Electrical
impedance spectroscopy (EIS) is used to study the effect of adding ATPase proteins to POPS:POPE bilayer lipid
membranes and correlate structural changes evident in the impedance data to the energy-conversion capability
of various partial and whole Biocell assemblies. The specific membrane resistance of a pure BLM drops from
40-120kΩ•cm2 to only a few hundred Ω•cm2 upon reconstitution of ATPase proteins. Power characterization
indicates that ATP hydrolysis may result in charging of the
silver-silver chloride electrodes.
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