BioEd Online

Scientists have managed to send and receive signals through a lipid membrane similar to the one that surrounds a living cell using silicon wires just 20-40 nanometres thick.

Their work could help to improve the integration of biological and electronic systems — allowing, for example, the development of electrical probes that can monitor what is happening inside a cell without damaging the cells or disrupting internal biological processes.

Combining biological and man-made components has proved tricky. In particular, no one has been able to use electronic devices to control the flow of ions through biological membranes, a crucial process in cell communication.

Now, a team led by Aleksandr Noy, a chemical biologist from Lawrence Livermore National Laboratory in California, has done just that by using a silicon nanowire embedded inside a lipid-bilayer membrane. The nanowire was also able to convert the flow of ions across the membrane into an electric signal. They report their findings this week in Proceeding of the National Academy of Sciences¹.

Others have coated nanowires or nanotubes with lipid membranes² — the negatively charged surface of silicon nanowires makes them hydrophilic, and therefore ideal templates for lipid bilayers — but this is the first time that researchers have managed to both send and receive signals through a biological membrane using electronic components. "The device can control the protein: open and close it, and the protein actions can change the device output." says Noy.

Switching channels

Noy and his team coated a silicon nanowire with a lipid bilayer then inserted a bacterial protein called gramicidin A into the membrane to form a channel through which protons and small positively charged ions could cross. As the protons started to flow, the researchers were able to record an electric signal in the nanowire. They could also regulate the signal reaching the wire by using calcium ions to block the channels, just as the ions do in living cells.

Next the team used alamethicin, a fungal protein that, like gramicidin A, inserts itself into the membrane to form a channel across it. By applying a voltage to the nanowire, the researchers were able to get the protein to assemble such that the channel opened and allowed ions to cross the membrane.

Kenneth Dawson, a chemical biologist from University College Dublin says this is important work. "What's really interesting — I was shocked by it — is that they were able to apply an electric field from the silicon wire to cause proteins to line up like in an organism — they were able to reconstitute the function of protein channels."

He, too, thinks that the device could lead to probes that can measure molecular contents and events in living cells.

"Nature is full of sophisticated proteins that do many fantastic things, and I think we should use these capabilities to build more sophisticated circuits that perform different functions," says Noy.

"We are still a way away from real, practical applications," he adds, "although the progress in developing nanowire devices and sensors has been staggeringly quick. If things work right, I could see practical applications within the next five years or possibly even sooner."