Carbon nanotubes have long intrigued physicists and engineers. Their microscopic size and tremendous strength make them ideal candidates for construction materials, and their conductive properties mean they can be used like wires in tiny electrical devices.

As manufacturing techniques and new research continue to drive these applications forward, A.T. Charlie Johnson, a professor in the Department of Physics and Astronomy in the School of Arts and Sciences, is riding the wave, pushing the boundaries of what carbon nanotubes can do in the field of biology.

Collaborating with researchers at the Monell Chemical Senses Center, Johnson has grafted biological components to carbon nanotube transistors, and has shown that they can be effective chemical sensors.

Last year, Johnson led a study in which researchers combined nanotubes with mouse olfactory receptors, the proteins on cells in the nose that detect the chemicals associated with smells.

Smelling and tasting are initiated when a chemical in the environment bings to a receptor on a cell in the nose or on the tongue. This act of binding causes a cascade of chemical reactions and nerve impulses that eventually register as the perception of a taste or a smell.  

In the olfactory study led by Johnson, instead of initiating a chemical cascade, the act of binding transmitted an electrical signal through the nanotube, allowing researchers to digitally register the concentrations of particular chemicals.   

In a more recent study, Johnson and his colleagues used similar principles in a different approach, wrapping tailored, single-stranded DNA sequences around nanotubes.

The order of the sequences created uniquely shaped pockets between the DNA and the nanotubes, making this device even more sensitive than the olfactory receptor model. It was able to differentiate between enantiomers, or chemicals that are mirror images of each other, as well as between chemicals that differed by a single atom. This precise detection gives researchers an unprecedented ability to identify the presence of specific molecules.  

Mammals, including dogs and even humans, are very good at innately making this sort of distinction, but artificial chemical detection systems have had limited success so far.

While further research is required to pinpoint what mechanisms are at work in these instances, Johnson and his colleagues are confident they can bring this nanotube technology out of the lab and into the real world.  

“We are looking to move in the direction of ‘real world’ chemical detection problems,” Johnson says. “For example, analyzing odors emitted by patients to determine whether or not they have a disease like skin cancer.”