Adenosine Triphosphate (ATP) is the ultimate energy of life. It’s the energy source that powers almost all living cells. Now, in research conducted by Alexandr Noy and colleagues at the Lawrence Livermore National Laboratory (California, USA), ATP is also an energy source for carbon nanotubes transistors that can eventually be used to link living tissue with man-made nanomachines.
Among the many roles available to carbon nanotubes is that of semiconductor. Semiconductor material in silicon form is a familiar basis for the electronics industry. Likewise transistors are one of the most fundamental components of electronic devices. Using carbon nanotubes for transistors is not a new idea, but adapting them for use within living tissue is new territory as is powering the transistors with ATP.
In this experimental work, the carbon nanotubes are rigged with electrodes at each end of the tube. An insulating layer of polymer (essentially, a plastic) covers all but the middle section of the nanotube. Then the entire nanotube device is coated with a specific lipid (fatty) bi-layer (two layers) that is similar to the lipids in living cells. The lipid bi-layer forms a membrane around the nanotube with a thin contact point in the middle section.
The coated nanotube is then immersed in a solution of ATP combined with sodium and potassium ions. When ATP comes in contact with the lipid bi-layer, a protein in the layer goes to work and begins moving sodium and potassium ions across the membrane onto the surface of the nanotube. As it works, the protein hydrolyses (splitting water molecules) the ATP and moves three sodium ions in one direction and two potassium ions in the opposite direction. The result is a net gain of one electron that is transferred to the nanotube. The nanotube acts as an ion pump transistor, collecting the charges and becoming a source of electrical energy.
Remember this is nano-scale, 1/100,000th the diameter of a human hair. The electrical charges involved are miniscule. Nevertheless, this is useful electrical energy that could eventually power various kinds of nano-devices, for example biological sensors and drug pumps.
The research paper is available behind the American Chemical Society paywall. Here is the abstract:
We report a hybrid bionanoelectronic transistor that has a local ATP-powered protein gate. ATP-dependent activity of a membrane ion pump, Na+/K+-ATPase, embedded in a lipid membrane covering the carbon nanotube, modulates the transistor output current by up to 40%. The ion pump gates the device by shifting the pH of the water layer between the lipid bilayer and nanotube surface. This transistor is a versatile bionanoelectronic platform that can incorporate other membrane proteins.