Tiny tango: Device sorts microscopic particles with speed and precision

by Steven Schultz
In a remarkable collaboration between engineers, physicists and biologists, Princeton scientists have invented a device that rapidly sorts microscopic particles into extremely fine gradations of sizes, opening a range of potential uses.

The researchers have used the device to sort particles ranging in size from bacterial cells to large segments of DNA and reported their results in the May 14 issue of Science. The technology could greatly accelerate the work of sequencing genomes and could find uses in many other areas, from improving the performance of pharmaceuticals to detecting bioterrorism agents.

Until now there was no way to sort large quantities of molecules or cells by size with such speed and precision, according to the researchers. Current methods separate particles only according to major differences in size and, for particles such as DNA, can take hours to perform. The Princeton invention can distinguish large quantities of particles that are 1.00 micrometer (a millionth of a meter) from others that are 1.005 microns in a matter of seconds.

The device is dubbed a "tango array" for the precise choreography it imposes upon particles.

The discovery was led by Lotien R. Huang, a postdoctoral researcher in electrical engineering, and grew out of a long-term collaboration between James Sturm, professor of electrical engineering, Robert Austin, a professor of physics, and Edward Cox, a professor of molecular biology, all of whom are co-authors of the Science paper. The group, which is part of the newly formed Princeton Institute for the Science and Technology of Materials, has produced a variety of devices for sorting DNA and other particles, but none as fast and precise as the tango array.

The trade-off between speed and precision had seemed insurmountable, said Huang, who has been building and testing sorting devices for nearly six years. The breakthrough came when a collaborator in the physics department, former postdoctoral researcher Jonas Tegenfeldt, challenged Huang to come up with a mathematical description of how his earlier attempts at sorting devices worked: If he altered a device, could he predict exactly how its performance would change?

"At first I thought such an analytical model would be impossible because the structures were so complicated, but Jonas got me thinking," said Huang, who has been working on the problem for six years. Within a few days, Huang not only derived a mathematical theory, but had an insight into making an entirely new device that has virtually no trade-off between speed and accuracy.

More details are available in a news release.