A team of neuroscientists at the RIKEN institute in Japan have created a liquid, primarily fashioned out of fructose sugar, that turns flesh transparent. This aqueous solution, called SeeDB, has been successfully used by the researchers to make mouse embryos and brains transparent without damaging any of the fine structures within the samples. The researchers were then able to visualize the entire neuronal circuitry of a mouse brain on a whole-brain scale, without having to first cut it into slices — an important first for neuroscience.
In technical terms, the RIKEN researchers have created an optical clearing agent. It’s somewhat hard to believe, but this clearing agent is essentially just a saturated solution of fructose (fruit sugar) in water, with some α-thioglycerol to prevent browning. Basically, a tissue sample — such as a mouse brain — is soaked in the fructose solution, and after three days it’s almost transparent. This occurs because the refractive index of SeeDB is 1.490, which is close to the refractive index of lipids (the fatty molecules that make up a lot of your body, including much of your brain’s gray and white matter). By matching the refractive index, the lipids essentially become transparent — and thus, as you can see in the images throughout this story, the entire sample becomes mostly transparent.