Transparent mice.
"The addition of common dye molecules that absorb in the near ultraviolet and blue regions improve optical transparency in nearby longer wavelengths. In essence, by causing sharp absorption in the blue region, the refractive index in the red part of the spectrum is increased without increasing absorption."
"By applying the Lorentz oscillator model for the dielectric properties of tissue components and absorbing molecules, we predicted that dye molecules with sharp absorption resonances in the near-ultraviolet spectrum (300 to 400 nm) and blue region of the visible spectrum (400 to 500 nm) are effective in raising the real part of the refractive index of the aqueous medium at longer wavelengths when dissolved in water, which is in agreement with the Kramers-Kronig relations. As a result, water-soluble dyes can effectively reduce the refractive index contrast between water and lipids, leading to optical transparency of live biological tissues."
The dye molecule they used? Tartrazine. Also known as "Yellow 5". Used in Doritos.
"So far, the scientists behind the new discovery have used the method to see the organs in a mouse's intact abdomen, glimpse the pulsing vessels surrounding a rodent skull, and to get an exceptionally clear view of muscle tissue through a microscope."
The dye in Doritos can make mice transparent | Popular Science
