Noninvasively focusing light deep inside living tissue could allow researchers to view brain cell activity, control the activity of neurons, and treat tumors deep inside the body. Living tissue, however, lacks “guide stars” at the target location that can provide feedback for focusing light inside tissue.

In a study published online on December 11, 2019, in Science Advances, Vladislav Verkhusha, Ph.D., and colleagues used a genetically encoded reversibly switchable bacterial phytochrome (RSBP) as a guide star for focusing light at specific locations in cells deep within living mice. The light could penetrate deeply into tissues because RSBPs work at the near-infrared (NIR) portion of the light spectrum, where photons are least interfered with by surrounding tissue.

The researchers used the technique to successfully focus on cells within tumors and brain tissue in living mice. The technique may be especially helpful in extending the range of photodynamic therapy (which chemically renders cells vulnerable to NIR light) to treat tumors deep inside the body. Dr. Verkhusha is professor of anatomy and structural biology and the Gruss Lipper Biophotonics Center at Einstein.