While people may have laughed at the mechanical-nose-bearing Odoradar device that Elmer Fudd once used to track Bugs Bunny, the development of real devices that can "smell" recently took a step forward, as researchers from the University of Pennsylvania grafted olfactory receptor proteins onto carbon nanotubes. These proteins are ordinarily located on the outer membrane of cells within the nose. When chemicals that enter the nose bind with the proteins, a cellular response is triggered, that leads to the perception of smell. It is hoped that a synthetic version of that same response could be possible, within sensing devices incorporating the nanotubes.
The proteins used by the Penn team came from mice, and like all olfactory receptors, are part of a class of proteins known as G Protein Coupled Receptors (GPCRs).
The researchers were able to create an interface between the proteins and a carbon nanotube transistor, which converted the chemical signals emitted by the proteins into electrical signals. Those signals could then conceivably be read by an electronic device, which would notify its user to the presence and concentration of a given chemical in the air.
While a Fudd-like sniffing device is certainly one application, project leader Prof. A.T. Charlie Johnson believes that medical applications are more likely. "GPCRs are common drug targets," he stated. "Since they are known to be very important in cell-environment interactions, they're very important in respect to disease pathology. In that respect, we now have a pathway into interrogating what those GPCRs actually respond to. You can imagine building a chip with many of these devices, each with different GPCRs, and exposing them all at once to various drugs to see which is effective at triggering a response."
Because pathogens often gain access to cells by attacking GPCRs, the technology could also be used to identify harmless chemicals that block and protect the receptors.
Although the proteins can't exist outside of a mouse's nose indefinitely, the scientists have been able to significantly lengthen their staying power. By embedding the proteins in nanoscale artificial cell membranes known as nanodiscs, the team were able to keep them going for two and a half months, as opposed to the single day that was the previous limit.
"The big picture is integrating nanotechnology with biology," said Johnson. "These complicated molecular machines are the prime method of communication between the interior of the cell and the exterior, and now we're incorporating their functionality with our nanotech devices."