Gabe Spalding at work in his lab assisted by Andrea Bulkley '06.

Illinois Wesleyan Physicist and St. Andrews University Colleagues Develop New Technique Using Light to Sort Cells

Dec. 3, 2003

BLOOMINGTON, Ill. — An Illinois Wesleyan University physicist and colleagues at the University of St. Andrews in Scotland have developed a new technique that uses light to separate microscopic particles such as biological cells.

Gabe Spalding, associate professor of physics at Illinois Wesleyan, along with Michael MacDonald and Kishan Dholakia from St. Andrews, reported the prototype of the new sorting machine in the Nov. 27 issue of Nature.

The technology has important implications for studies of drug delivery at the cellular level, among other potential applications. The system could evolve into an inexpensive component for "lab-on-a-chip" systems used in physical and biomedical research.

"We have found this system to be simpler, more sterile, and far less expensive than existing techniques for sorting microscopic materials. It is also extremely accurate and has potential for biomedical and other commercial applications," said Spalding, who spent a sabbatical leave from Illinois Wesleyan working with MacDonald, Dholakia, and other scientists at St. Andrews.

In its study, the team used light to sort and separate protein microcapsules, which are used in drug delivery and biomedicine. The microcapsules were directed through a three-dimensional lattice, or grid, created by an interference pattern of many laser beams. As objects moved through the grid, they demonstrated a different likelihood of being grabbed by the bright spots of the pattern. By adjusting both the rate at which the particles flowed and the light pattern, some of the microcapsules flowed through while others were channeled off to an uptake stream.

"By passing these microcapsules through the optical lattice, we were able to sort out the one size that would be used for controlled drug delivery," explained Spalding. "Having that level of control is critical, and our process has been 96 percent efficient."

Spalding said that the optical method is faster and more efficient than currently available methods of on-chip cell sorting such as gel electrophoresis, which was used in the Human Genome Project, or fluorescence-activated cell sorting known as FACS.

"Our technology has major advantages over both existing methods," said Spalding. "FACS works with only fluorescent particles and is expensive and complex. The gel electrophoresis is extremely slow and requires batch processing. Not only does our optical lattice permit continuous processing, which is much faster, but this system also avoids jamming and is compatible with the ‘lab-on-a-chip’ technologies."

Among the various applications that the team envisions for this technology is the ability to have a medical patient supply a small sample which the system could sort and diagnose in real time.
Thus far, the team’s work has involved material that ranges from a single cell down to about a tenth of that size. "For material in this range, our procedure is immediately applicable. There are a lot of different biological tests where you need to sort cells," said Spalding. "We need to do more work to find how well this technique will continue to function as we shrink down to smaller size scales."

The work was funded by Research Corporation, the National Science Foundation, and the UK Engineering and Physical Sciences Research Council and was performed in the Optical Trapping Group in the School of Physics and Astronomy at St. Andrews.