January 2000

Sorting Out Life

Continued from page 1

By Rebecca Zacks

The microFACS uses laser light and electricity to sort a cell mixture. Three 2-millimeter-wide wells on the chip are connected by a T-shaped network of channels. A researcher first tags the cells with fluorescent markers, then loads them into the bottom well and drives them toward the channel junction with an electric current. The channels narrow to just a few micrometers near the junction, forcing the cells to proceed in single file. A laser aimed at the junction hits the different markers and causes each cell type to fluoresce in a particular color-say, red for tumor and blue for normal. A detector prompts a computer to adjust the current to drive each cell to the left or the right, into a waste well or a collection well.

One reason the microFACS is so cheap is that the chips are made by soft lithography, an experimental process developed by Whitesides. It's potentially far less expensive than micromachining; instead of carving individual chips, researchers cast them in a reusable silicon mold.

Whitesides calls Quake's cell sorter "an elegant piece of design," and points out that it could be coupled to other ultrasmall analytical systems, such as single-cell DNA sequencers. Indeed, one of Quake's future aims is to build the sorter and all the other scaled-down devices needed for a particular experiment linked together on one chip, a goal that many others in the field are hotly pursuing.