US scientists have developed a microfluidic-based platform that screens thousands of cells at once and could be used to identify rare cells behaviour to help cancer and stem cell biology research, they claim.

Tens of thousands of odorant molecules can be discriminated by the sense of smell. Olfactory sensory neurons (OSNs) in the nose translate odorant chemical signals into unique neuronal signals that guide many important behaviours. Odours activate odorant receptors (ORs) of which there are over 1000 types in mice. Each OSN expresses only one type of OR but the large numbers have made it impossible to analyse odour response across all OSN-OR types using current techniques.

Now Albert Folch at the University of Washington, Seattle and his team have developed a method to screen over 20 000 single cells at once in a microwell array. Using calcium imaging they were able to detect and analyse odorant responses of thousands of mouse OSNs simultaneously, explains Folch, enabling cells with rare patterns of response to be found.

Folch compared the OSN responses to four different fruity smells (vanilla, rose, berry and banana) in one experiment. Using calcium imaging, the neurons responses were identified by measuring the change in fluorescence signals. Folch explains that using microwells to place thousands of OSNs in the field of view of a camera means that all the ORs should be represented in the sample. 'I believe these microarrays are very powerful for finding rare cells that display particular patterns of responses that would be impossible to find by other means' he says.

Tim Holy, who researches olfactory systems in mice at Washington University in St. Louis, US, comments 'This is an elegant new approach to record from many neurons simultaneously under well-controlled stimulus conditions.'

Folch says the team would ultimately like to develop a system where the cells are exposed to odours in the gas phase. 'I suspect, but have not been able to prove yet, that many of the problems with OSN viability and smelling/adaptation artifacts come from the fact that the odorants (most of them water-insoluble) are artificially solubilised in water' he adds.