Artificial Nano Nose Sniffs out Cancer Cells

In most mammals' case, the nose is the primary organ for smelling. As the animal sniffs, the air flows through the nose and over structures called turbinates in the nasal cavity. The turbulence caused by this disruption slows the air and directs it toward the olfactory epithelium. At the surface of the olfactory epithelium, odor molecules carried by the air contact olfactory receptor neurons which transduce the features of the molecule into electrical impulses in the brain.

Dogs have one the most advanced noses in the animal kingdom. They have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren.

This makes them very useful to humans, since they can be trained to sniff out drugs, explosives, predators and game during hunting and they can even detect the onset of medical conditions like epilepsy and psychiatric disorders of their impaired owners, thus helping them deal with various situations.

Vince Rotello and his colleagues from the University of Massachusetts, US applied the same principle to detect proteins with the use of an artificial nano nose.

A set of gold nanoparticles with various coatings can identify proteins by mimicking the way the human nose distinguishes scents. Researchers are using them to detect signs of illness in bodily fluids.

"In your nose there are a variety of receptors that all react in slightly different ways to compounds," says Vince Rotello. Instead of having a specific sensor for each smell, the nose responds to the pattern of responses produced by multiple, generalized receptors.

This is the first system capable of identifying larger and more complicated molecules, like proteins.

There are six receptors in the new "nano nose". Each consists of a solution containing gold nanoparticles measuring 2 nanometres across, with different coatings. The coatings are made from slightly different organic molecules containing nitrogen atoms.

Different proteins will bind to multiple receptors but attach more easily to some than others. The team measured these binding properties using a fluorescent signal molecule that attaches to the receptor particles but is displaced by a protein when it binds.

The more this molecule is displaced, the more light it produces. A computer then analyzes the relative strengths of these light signals.

Rotello says the applications could be useful for detecting diseases. Instead of looking for a single specific marker molecule, it would sniff out an imbalance in the usual combination of proteins in body fluids.

"We want this nose to be able to say, 'I smell something funny'," he explains.

Early results, with blood plasma from sick and healthy lab animals, have been promising. "We can detect changes in serum and are working on making that ability statistically robust," says Rotello. "Later we can start working out which 'smells' point to particular kinds of cancer or other diseases."