Using blood proteins to make living brains transparent

Making a living brain transparent and watching its neurons fire without disrupting their function – sounds like science fiction, doesn’t it? However, the solution may already exist within our bodies.

In a study published in Nature Methods On March 12, 2026, a research team led by Kyushu University presents a new reagent called SeeDB-Live. It uses albumin, a common protein in blood serum, to clear tissue while maintaining cell function. The technique allows scientists to see deeper, brighter structures in both brain slices on a dish and in live mice, reaching neural activity previously unseen.

This is the first time that tissue purification has been achieved without altering its biology.”

Takeshi Imai, Senior Study Author and Professor, School of Medical Sciences, Kyushu University

“SeeDB-Live can pave the way for live deep web visualization, both ex vivo and in vivoadded the study’s first author, assistant professor Shigenori Inagaki of the same school.

How to see deeper into the living brain?

Complex functions such as memory and thinking arise from real-time communication between cells deep in the brain. Although the slices retain some activity, understanding the physiological dynamics of the brain requires imaging of the living brain.

Making the opaque brain transparent is one solution, and it starts with optics.

Think glass marbles: visible in air but almost disappear in oil. This is because light refracts and scatters when it passes through materials with different refractive indices, and brain tissue behaves the same way. Lipids and other cellular components create microscopic mismatches, scattering light, obscuring deeper structures. Reduce them and the light travels evenly.

Through systematic experiments, Imai’s group found that living cells become more transparent when the refractive index of the extracellular solution is adjusted to 1.36-1.37.

With a precise goal in hand, the team needed a non-toxic way to reach it while maintaining osmotic balance so that the cells neither swell nor shrink. Previously they tried natural substances such as sugarbut these required high concentrations which increased the osmotic pressure and dehydrate the cells.

As osmotic pressure depends on the number of molecules, the team turned to large spherical polymers. Their larger size means less is required to increase the refractive index, which adjusts optical performance without overwhelming the cells. However, despite testing nearly 100 compounds, the answer refused to come.

A blood protein is the surprising key to brain transparency

The turning point came unexpectedly.

Late one night, Inagaki returned to a simple idea: proteins are polymers. He grabbed a bottle of bovine serum albumin (BSA), a common laboratory reagent derived from blood, which, to his surprise, showed the lowest osmotic pressure at the desired refractive index.

“I tried it three or four times before I believed it,” Inagaki recalls. Alone in the lab that night, he let out a cry of excitement. “Of all things, we never expected it to come to this.”

By adding albumin to the culture medium to match the refractive index inside the cells, the team developed a living tissue clearing solution, which they called SeeDB-Live.

“During the development of SeeDB-Live, we discovered that neurons are extremely sensitive to ion concentrations, and it took a huge amount of effort to get the formulation right. Thanks to that lucky night alone in the lab, I helped myself to an expensive, high-purity BSA that I normally wouldn’t have dared to use,” he adds with a laugh.

SeeDB-Live renders mouse brain slices transparent within one hour of immersion. When combined with a calcium marker, normal neuronal firing deep within the tissue was illuminated in the transparent brain slice. When applied to living mouse brains, fluorescence signals from deep neurons became three times brighter.

This opens up clear views of layer 5 of the cerebral cortex, where richly branching neurons help reveal how the brain processes information and converts neural activity into action. Before SeeDB-Live, sharp images at this depth were difficult to obtain with conventional strategies.

Furthermore, as the extracellular fluid washes away SeeDB-Live within a few hours, tissue transparency returns to its original state. Because the method does not cause permanent changes, the same mouse can be imaged repeatedly to track brain activity over time.

“Albumin is abundant in blood and highly soluble, which makes it suitable for dialysis,” notes Imai. “It was an accidental discovery, but looking back, it’s almost natural. What evolution has shaped over millions of years is really impressive.”

A decade after you said “impossible”

SeeDB-Live demonstrates the first non-invasive optical cleanup that significantly increases imaging depth and enables observation of tissue-wide dynamics.

The researchers expect it to enhance deep fluorescence imaging for understanding the brain’s integrative functions. It can also help evaluate 3D tissue and brain organoids for drug discovery research.

The team notes that although SeeDB-Live works well for brain tissue, biological barriers limit delivery to other organs, and access to the brain still requires a surgical window that can cause stress and reduce efficiency.

“I feel like we haven’t realized its full potential yet,” says Inagaki, adding that future efforts will focus on less invasive delivery methods to improve penetration for deeper imaging and better functional analysis of brain activity.

For Imai, the achievement marks the culmination of more than a decade of work. After developing SeeDB in 2013 and SeeDB2 in 2016 for fixed tissue, he was repeatedly asked if it was possible to clean live tissue.

“That question came to me about a hundred times, and every time I answered ‘impossible,'” Imai reflects. “But ten years later, here we are. When something seems impossible, if you keep thinking about it, you might eventually find a way.”