A method of producing smell receptors in the laboratory has been developed by biological engineers at the Massachusetts Institute of Technology (MIT). This development has raised the possibility of creation of "artificial noses" for use in a variety of settings.
The breakthrough may also be helpful in discerning how the senses of smell can recognize a seemingly infinite range of odours, say the researchers.
"Smell is perhaps one of the oldest and most primitive senses, but nobody really understands how it works. It still remains a tantalizing enigma," said Shuguang Zhang, associate director of MIT's Center for Biomedical Engineering and senior author of a paper on the work appearing online this week in the Proceedings of the National Academy of Sciences (PNAS).
He and his colleagues believe that artificial noses can provide an alternative to drug- and explosive-sniffing dogs, apart from having numerous medical applications.
The researchers have already secured funding from DARPA for its RealNose project.
To date, scientists have struggled to understand the molecular basis of smell due to the difficulty in working with the proteins that detect odors, known as olfactory receptors.
"The main barrier to studying smell is that we haven't been able to make enough receptors and purify them to homogeneity. Now, it's finally available as a raw material for people to utilize, and should enable many new studies into smell research," said Brian Cook, who just defended his MIT PhD thesis based on this work.
Liselotte Kaiser, lead author of the paper, points out that olfactory receptors are highly hydrophobic (water-fearing) and lose their structure when placed in water-based solutions, a reason why it is very difficult to isolate them in quantities large enough to study them in detail.
However, Kaiser and others now claim to have developed a method to isolate and purify the proteins by performing each step in a hydrophobic detergent solution, which allows the proteins to maintain their structure and function.
Their technique involves a cell-free synthesis using commercially available wheat germ extract to produce a particular receptor, after which the protein is isolated through several purification steps.
The researchers say that their method can rapidly produce large amounts of protein, enough to start structural and functional studies.
The team also use a similar method, which uses engineered mammalian cells, to produce the receptors.
Although that method takes more time and labour than the cell-free approach, it could have advantages in that the receptor is processed more naturally.
The MIT researchers now plan to join forces with scientists worldwide to develop a portable microfluidic device that can identify an array of different odours.
They think that such a device can be used in medicine for the early diagnosis of certain diseases that produce distinctive odours - like diabetes and lung, bladder and skin cancers.