Pee-Ew! Scientists Create Carbon Nanotube–Based Sensor with a Sense of Smell

In the quest to integrate biological molecules with nanotechnology, a group of researchers at the University of Pennsylvania (Philadelphia), University of Miami, University of Illinois at Urbana-Champaign, Princeton University (Princeton, NJ), the Monell Chemical Senses Center (Philadelphia), Evolved Machines (Palo Alto, CA), and Nanosense Inc. (Redwood City, CA) have developed a a carbon nanotube-based transistor that incorporates olfactory receptor proteins (ORs). Seeking to create electronic devices with a sense of smell that could eventually replace the use of animals to sniff out drugs or bombs, the scientists also hope to develop olfactory electronic devices for performing disease diagnosis.

According to Nanowerk, the researchers began by purifying ORs from cells and then solubilized them in two distinct nanoscale constructs: digitonin micelles and engineered, stable, self-assembling nanoscale membrane assemblies known as nanodiscs. Then, they attached these solubilized ORs via a polyhistidine tag to high-quality nanotube transistors that were previously functionalized with nickel-nitrilotriacetic acid

"After integration with nanotube transistors, the ORs retain their biological functionality for odorant binding, while binding events are read out electronically by the nanotube transistors," Charlie Johnson, professor in the department of physics and astronomy at the University of Pennsylvania, tells Nanowerk. "Our OR-nanotube hybrids show responses to vapor analytes that agree with the responses of the ORs when they are expressed in a 'heterologous system', that is, a cell system (frog eggs, in our case) that is different from the organism that the ORs are derived from (we used mouse ORs).

The scientists were interested in fabricating bioelectronic hybrids they exhibit a carefully designed chemical linkage between the OR and the nanotube device and an engineered membrane-like environment for the OR, according to Johnson. These more-complex strategies for housing the OR and coupling it to the nanotube transistor enabled the researchers to demonstrate nanotube-OR hybrids with vapor responses that show strong agreement with the responses measured in another cell system.