Dye makes tissue temporarily transparent

By applying a solution of tartrazine dye—a vibrant yellow food coloring—to a mouse’s skin, researchers were able to see through that opaque tissue. The transformation to transparency is temporary. A simple wash with water removes the dye and the effect. The technique, which has not been tested in people, could help biologists study living systems and might make some medical procedures less invasive. A team led by Stanford University’s Mark L. Brongersma and Guosong Hong used light scattering to develop the technique. The refractive index of water in cells differs dramatically from the indexes of biological molecules like lipids and proteins. This variation makes light scatter and is one of the reasons that skin appears opaque. Tartrazine absorbs light in just the right region of the spectrum to change the refractive index of water so that it more closely matches those of biological molecules. This prevents light from scattering and