Lasers Help Identify Biological Targets

July 1, 2014
Lasers Help Identify Biological Targets
This microfluidic device is similar to the one used for the new high-throughput sorting system.

It can be incredibly time consuming to scan biological fluids looking for tumor cells or other disease markers. One reason: The offending cells typically exist at concentrations of just parts-per-million. But the task could be simplified and accelerated by a factor of 100 if researchers at the Massachusetts Institute of Technology can bring their new sorting technique to market.

Scientists usually count or sort fluids by sending them through small channels and using machine vision and microscopes. If the fluid flow is sped up in conventional processing equipment, it becomes turbulent, making identification of cells and markers impossible. The researchers discovered that adding hyaluronic acid could let the fluid’s Reynolds number go as high as 10,000 without causing turbulence. (Fluid flows normally cannot exceed 2,400 without creating turbulence.) Hyaluronic acid acts as a lubricant in the knee and is harmless to biological samples.

The new additive increased fluid flow, but the relatively soft materials used to make microfluidic channels and devices would not withstand the higher pressures. So the team had to develop a more-rigid microfluidic-handling device out of epoxy that was still transparent.

In the prototype device, fluids travel through channels 50-µm wide at more than 400 mph. Cells and other particles are forced to the center of the fluid flow and travel single file through the channels. A laser emits flashes measuring 10 billionths of a second to illuminate particles, letting the team image the size, shape, and orientation of cells.

The sorting technique could be refined for use in medical diagnostics, water purification, and even industrial separation for biofuel production.

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