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Biocavity Laser Could Fill a Void

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Hank Hogan

Today's surgeons are, in some ways, blind. Because they can't see how deep cancer cells may have spread, during an operation they remove not only the tumor, but also the surrounding tissue. If a biopsy indicates

malignancy is still present, the patient must again go under the knife. For some cancers, like those of the brain, the process may be repeated several times because the surgeon is under great pressure not to remove too much tissue.

Paul Gourley, a staff member at Sandia National Laboratories, may have solved this problem by creating a biological microcavity laser, a tool that allows the surgeon to detect the presence of cancer cells as he cuts away the tissue.

A dime-size microcavity laser promises to help surgeons determine when they can stop cutting while removing a cancerous tumor. It detects the difference between healthy and malignant cells.

"You can see the cells that are undergoing synthesis, so it shows up as a very different distribution," Gourley said. He explained that prior to dividing, cells exist in a state where they have basically double the normal amount of DNA. Typically, you wouldn't see very many cells in this state because normal cells grow very slowly. But cancer cells divide and grow rapidly, so that if cancer were present, cells in this state would be in abundance.

The detection process begins with the insertion of cells into a microcavity. Without a cell present, the laser is below threshold and emits no coherent light. When a cell is introduced, lateral optical confinement occurs and the laser emits a near-IR beam. Thus, the laser automatically registers the presence of a cell.

A very important additional feature, key to detecting cancer, is that the laser output from a malignant cell is shifted from that of a normal cell. Because the malignant cells replicate faster, producing more DNA and protein, they exhibit a higher optical density or refractive index. This increase in optical density slows the speed of light in the cavity and shifts the lasing frequency. Shuttling cells into and out of the microcavity with microfluidic technology allows a large number of cells to be analyzed quickly.

With the dime-size biological microcavity device, Gourley has proved that only a few hundred cells are needed for analysis. The technology could be 10 to 100 times less expensive and five times faster than the current approach, which is not in real time and which must be done outside of surgery. Eventually, the technique could be incorporated into a small vacuum device to scoop up tissue for real-time analysis. Commercialization is several years away because of such issues as sample preparation, device sensitivity and regulatory approval.

When that happens, surgeons might have a diagnostic tool that could incorporate other tests as well. "It's compatible with other kinds of technologies that rely on microfluidics and microsampling of molecules," Gourley said.

Photonics Spectra
Jun 2000
industrialResearch & TechnologyTech Pulse

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