"You can remove a cell with high precision in 3D without damaging the cells above and below it", Adela Ben-Yakar stated. "And you can see, with the same precision, what you are doing to guide your microsurgery."
Femtosecond lasers produce extremely brief, high-energy light pulses that sear a targeted cell so quickly and accurately the lasers' heat has no time to escape and damage nearby healthy cells. As a result, the medical community envisions the lasers' use for more accurate destruction of many types of unhealthy material. These include small tumours of the vocal cords, cancer cells left behind after the removal of solid tumours, individual cancer cells scattered throughout brain or other tissue and plaque in arteries.
A commercially available femtosecond laser system and microscope was developed recently for LASIK and other eye surgeries, but the system's bulk limits its usefulness. Adela Ben-Yakar's laboratory has overcome technological challenges to create a microscope system that can deliver femtosecond laser pulses up to 250 microns deep inside tissue. The system includes a tiny, flexible probe that focuses light pulses to a spot size smaller than human cells.
Adela Ben-Yakar's experimental system and its use to destroy a single cell within layers of breast cancer cells grown in the laboratory is described in the June 23 issue of Optics Express. Within a few years, Adela Ben-Yakar expects to shrink the probe's 15-millimeter diameter three-fold, so it would match endoscopes used today for laparoscopic surgery. The probe tip she has developed also could be made disposable for use operating on people who have infectious diseases or destroying deadly viruses and other biomaterials.
To develop the miniature laser-surgery system, Adela Ben-Yakar worked with co-author Olav Solgaard at Stanford University's Electrical Engineering Department to incorporate a miniaturized scanning mirror. Adela Ben-Yakar and her graduate student Chris Hoy, another co-author, also used a novel fiber optic cable that can withstand intense light pulses traveling from an infrared, femtosecond laser. To make the intensity more manageable, they stretched the light pulses into longer, weaker pulses for traveling through the fiber. Then they used the fiber's unique properties to reconstruct the light into more intense, short light pulses before entering the tissue.
For the study, Adela Ben-Yakar directed laser light at breast cancer cells in three-dimensional biostructures that mimic the optical properties of breast tissue. She has since studied laboratory-grown, layered cell structures that mimic skin tissue and other tissues.
Adela Ben-Yakar is also investigating the use of nanoparticles to focus the light energy on targeted cells. In research published last year, she demonstrated that gold nanoparticles can function as nano-scale magnifying lenses, increasing the laser light reaching cells by at least an order of magnitude, or 10-fold.
"If we can consistently deliver nanoparticles to cancer cells or other tissue that we want to target, we would be able to remove hundreds of unwanted cells at once using a single femtosecond laser pulse", Adela Ben-Yakar stated. "But we would still be keeping the healthy cells alive while photo-damaging just the cells we want, basically creating nanoscale holes in a tissue."
Grants from the National Science Foundation and the National Institute of Health funded the research.