Carbon nanotubes, rolled-up lattices of carbon atoms, are highly conductive and sensitive to electrical charge, making them promising components of nanoscale electronic devices. By attaching different biological structures to the exteriors of the nanotubes, they can function as highly specific biosensors. When the attached structure binds to a molecule, that molecule's charge can affect the electrical conduction of the nanotube, which can be part of an electrical circuit like a wire. Such a device can therefore provide an electronic read-out of the presence, or even concentration, of a particular molecule.
To get the electrical signal out of these nanotubes, the team first turned them into transistor devices.
"We first grow these nanotubes on what amounts to a large chip using a vapor deposition method, then make electrical connections essentially at random," Johnson said. "We then break up the chip and test all of the individual nanotube transistors to see which work the best."
In their recent experiment, Johnson's team attached antibodies that naturally develop in most animals that are infected with the Lyme disease bacterium to these nanotube transistors. These antibodies naturally bind to an antigen, in this case, a protein in the Lyme bacterium, as part of the body's immune response.
"We have a chemical process that lets us connect any protein to carbon nanotubes. Nanotubes are very stable, so we have a very reactive compound that binds to the nanotube and also has a carboxylic acid group on the other end. For biochemists, getting any kind of protein to bind to a carboxylic acid group is just child's play at this point, and we have worked with them to learn how to perform this chemistry on the side wall of nanotubes. "
After using atomic-force microscopy to show that antibodies had indeed bound to the exteriors of their nanotube
|Contact: Evan Lerner|
University of Pennsylvania