lab fab
A portable protein nanopore Lipid bilayer stabilization allows nanopore sensing to step outside the lab.
P
ing purposes because it forms a very Ingo Köper of the Max Planck Instirotein nanopores have a reputation tight electrical seal, but we needed to tute for Polymer Research (Germany) is for being fragile. So, despite the investigating a competing technology great applications that researchers imag- find a way to stabilize it.” Bayley and colleagues stabilized a that tethers a lipid bilayer to a solid supine—including the detection of environlipid bilayer containing a single aHL port. Solid-supported bilayers exhibit mental pollutants or chemical weapons enhanced stability, but singleand ultrarapid DNA sequencchannel measurements are not ing—their practical use has yet possible. Köper says, “The been limited. Now, Xiao-feng fragility of the unsupported Kang, Hagan Bayley, and collipid membrane has been its leagues at Texas A&M Unimajor drawback in practical versity and the University of applications. The work of Oxford (U.K.) have found a Bayley and co-workers is a solution. The team recently step forward.” introduced a storable, portaAccording to David Deamble bilayer chip containing a aHL nanopore Teflon er of the University of Califorsingle protein nanopore ( J. Gel Lipid bilayer Plastic nia Santa Cruz, a storable biAm. Chem. Soc. 2007, 129, layer chip will increase the 4701–4705). productivity of protein nanoResearchers typically pore sensing experiments. embed a single Staphylococcus “Right now it takes a couple aureus a-hemolysin (aHL) nanopore into a planar lipid of hours to set up a bilayer A Teflon septum with an aperture is glued between two plastic bilayer. The bilayer is formed with a nanopore, and it’s across an ~100-µm-diam aper- films, each with an orifice. The orifice is filled with unpolymerized good maybe for a couple agarose, and a lipid bilayer with a single protein nanopore is ashours of use,” he says. “If we ture in a Teflon film. Ionic sembled in the Teflon aperture. The agarose is then allowed to had a single pore that could current passing through the aHL nanopore—which can polymerize, stabilizing the bilayer. Components are not to scale. be reused on multiple days, be bioengineered to display that would be a huge timeanalyte binding sites on the inside—is nanopore by assembling the bilayer in saver.” Deamer envisions many potential measured when a voltage is applied the presence of low-melt agarose. When applications for a portable protein nanoacross the bilayer. The ionic current the temperature was decreased, allowing pore chip, including the rapid identificachanges in response to partial blockage the agarose to polymerize, a thin layer tion of microbial species, bioterrorism of the nanopore at these sites by anaof gel encapsulated the lipid bilayer con- agents, and pandemic viruses. lytes, which can include cations and antaining the aHL nanopore. The agarose According to Bayley, an additional ions, small organic molecules, and sinlayer was protective but thin enough to advantage that lipid bilayer stabilization gle-stranded DNA. By analyzing the allow rapid diffusion of small molecules provides for nanopore sensing is that it degree, frequency, and duration of ionic to the nanopore. will allow the commercialization of bicurrent variation, researchers can identiThe researchers went on to find that layer chips. Not only could the agarosefy and quantify analytes. the conductance of the nanopore was encapsulated bilayer chip be used for But the planar lipid bilayers used in the same in polymerized agarose as in analyses in the field but it could also be conventional protein nanopore experiaqueous solution. The bilayer chip shipped and stored. Bayley says, “It’s ments are extremely fragile; they remain could be stored at 4 °C for at least 3 not so difficult to make a bilayer in the intact for only a few hours and cannot weeks. In contrast to unprotected bilaylab, but you simply can’t carry the curbe transported. Bayley says, “Many peo- ers, the agarose-encapsulated bilayer rent recording equipment around becould be removed from the recording ple think it’s the protein nanopore cause the bilayer will break immediately. that’s unstable, but it’s actually the lipid chamber and reused at least three times. The encapsulated bilayer chip is far bilayer that is the Achilles’ heel of nano- In addition, the encapsulated bilayer more rugged and is just the thing for pore sensing technology. The bilayer is chip was much more resistant to meuse outside the lab.” a ideal for single-channel electrical record- chanical disturbances. —Laura Cassiday © 2007 AMERICAN CHEMICAL SOCIETY
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