New label-free imaging method created to visualise brain samples

Researchers have developed a new label-free imaging method to visualise brain slices. The technique was created by scientists from South Korea, including Korea University, who enhanced the regional heterogeneity of the optical properties using the tissue clearing principle. 

According to the researchers, optical clearing has emerged as a powerful tool for volume imaging. Although volume imaging with immunostaining have been successful in many protocols, obtaining homogeneously stained thick samples remains challenging. 

“Acquiring high-resolution images from thick samples in light microscopy has been considered to have great limitations owing to the light scattering due to the high lipid contents and the opaque, dense extracellular matrix (ECM) in thick tissues,” the researchers write in their paper. 

To address these issues, the team used FxClear, a method for delipidation of brain tissue, to retain a larger proportion of lipids at the white matter. They found that the embedding media affected the contrasts for the lipid-rich or ECM-rich areas, depending on their chemical properties.

This allowed the researchers to tailor the clearing conditions for the enhancement of the refractive indices (RIs) differences between grey and white matter, or several pathological features. RI differences could then be imaged using conventional light microscopy or optical coherence tomography.

The team used their new technique to show that nerve bundles in a normal brain, brain trauma-induced tissue fibrosis and misfolded proteins accumulate to form amyloid plaques in an Alzheimer’s mouse model brain. These were sensitively recognised without any labelling.

Furthermore, they discovered that the use of different RI adjusting media provided differential responses in biological specimens. This presents an additional consideration for the development of diagnostic strategies based on label-free optical imaging using the differences in RI.

“We propose that our protocol is simple, reliable and flexible for label-free imaging, easily implementable to routine histology laboratory,” say the researchers in their paper. 

The results of the study are published in iScience.