Sorting individual cells is not a problem, but what if a researcher wants to sort clusters of cells, or even whole embryos?

Union Biometrica of Holliston, Massachusetts, offers a potential solution in the shape of its COPAS family of instruments. These, it says, can work with objects ranging from pancreatic islets up to zebrafish hatchlings. The principle is similar to fluorescence-activated cell sorting (FACS) — objects in solution pass through a specially designed flow-cell, where they are optically profiled according to as many as five different sorting parameters (which can include three fluorescent wavelengths), and specimens of interest are diverted and collected.

But some design adjustments were necessary to protect the integrity of the multicellular objects being sorted. For one thing, rather than using charge-based sorting of droplets, COPAS uses rapid puffs of air to gently divert ‘slices’ from the flow stream that contain objects of interest.

COPAS also uses lower flow-rates than FACS, sorting between 100 and 300 objects per second. “We sacrifice speed for gentle flow, which results in increased viability and less destruction of what we're analysing,” says Rock Pulak, Union Biometrica's director of life sciences. “It's still much faster than trying to analyse these same numbers of cell clusters by microscope.”

Union Biometrica's BioSorter COPAS can sort clusters of cells. Credit: UNION BIOMETRICA

In addition, the lower speeds mean that it is possible to do limited analysis of fluorescence localization within the objects being sorted. Pulak speculates that future instruments may even be able to perform actual imaging during the sorting process.

Sometimes even single cells prefer a lighter touch, and an ongoing collaboration between the company and the Joslin Diabetes Center in Boston has shown that COPAS is also useful for sorting adipocytes and hepatocytes.

“These are larger cells that are very delicate and subject to sensitivities with respect to shear force,” says Pulak. “We are finding that our technology is appropriate for these kinds of applications.”

M.E.