The Incredible Shrinking Laboratory -- Flow Cytometry on a Chip

Cal Tech scientists have rolled out the latest in what is turning out to be a long line of miniaturized laboratory devices—the µFACS. The µFACS is a miniaturized flow cytometer that can sort fluorescent cells and particles in a fraction of the space (and for a fraction of the money) used by convention flow sorting devices. Stephen Quake, professor of applied physics, and colleagues report on this new instrument in the November issue of Nature Biotechnology.

The µFACS uses electro-osmotic flow to move cells or particles along 3 µm-channels etched in a silicone-elastomer chip. Mounted on an inverted microscope, the chip is excited by a laser beam focused on the channel near a T-shaped junction (see figure). The signal is collected by a PMT, and once a threshold fluorescence level is recorded, the cell is diverted by a shift in the voltage to a collection well.

The researchers report several examples of sorting done with their petite FACS—a mixture of red and blue fluorescent beads, 1 µm in size, were sorted into single color pools with nearly 100-fold enrichment. In addition, live E. coli expressing green fluorescent protein mixed with various amounts of wild type E. coli were enriched 30-fold through sorting. Although they report the viability of the sorted E. coli at only 20%, as defined (number of colonies/number of fluorescent events recorded) this figure folds recovery into viability, and hence, viability may be better than it appears.

The µFACS offers a number of advantages beyond the obvious. It requires tiny amounts of material—the detection volume is in the femtoliter range—which not only saves on material, it also reduces the amount of background fluorescence, allowing greater sensitivities. A number of the technically troubling aspects of flow cytometry—droplet creation, aerosol formation, sterilization, and cross-contamination—are not an issue with this disposable FACS. In addition, it can be easily configured for parallel sorting, which will make it faster and allow sorting on multiple parameters.

For more information: Stephen R. Quake, Department of Applied Physics, California Institute of Technology, Pasadena, CA 91125. Email: quake@its.caltech.edu

By Laura DeFrancesco