Scientists created a novel method for enlarging brain tissue samples, allowing for high-resolution imaging.
The technique uses inexpensive and easy to acquire chemicals and microscopes, including an absorbent material commonly found in diapers, MIT reported.
"Instead of acquiring a new microscope to take images with nanoscale resolution, you can take the images on a regular microscope. You physically make the sample bigger, rather than trying to magnify the rays of light that are emitted by the sample," says Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT.
Conventional microscopes use lenses to focus light emitted from a sample and transform it into a magnified image, but this process comes with limits. This phenomenon is known of as the diffraction limit, meaning the method cannot be used to image objects smaller than the wavelengths of light being used. Researchers have come up with some tricks to get around these limitations, but they work best on small samples and often take a long time to process.
"If you want to map the brain, or understand how cancer cells are organized in a metastasizing tumor, or how immune cells are configured in an autoimmune attack, you have to look at a large piece of tissue with nanoscale precision," Boyden said.
To achieve this, the researchers focused on the samples themselves instead of the microscopes used to image them. They embedded the tissue in an expandable polymer gel made of polyacrylate. Before enlarging the tissue, the team labled the cell components or proteins they wanted to examine using a binding antibody "dye." Once the parts were labeled, the researchers applied polyacrylate gel and heat to form a gel and then digest the binding proteins to allow the sample to be enlarged.
"What you're left with is a three-dimensional, fluorescent cast of the original material. And the cast itself is swollen, unimpeded by the original biological structure," said researcher Paul Tillberg.
Through this method the team was able to image a section of brain tissue 500 by 200 by 100 microns with a standard confocal microscope, which would not have been possible with current imaging methods.
"The exciting part is that this approach can acquire data at the same high speed per pixel as conventional microscopy, contrary to most other methods that beat the diffraction limit for microscopy, which can be 1,000 times slower per pixel," said George Church, a professor of genetics at Harvard Medical School who was not part of the research team.
The researchers hope this new groundbreaking method will help scientists image brain cells, revealing how they connect with each other across larger regions of the brain.
"There are lots of biological questions where you have to understand a large structure," Boyden said. "Especially for the brain, you have to be able to image a large volume of tissue, but also to see where all the nanoscale components are."
Other possible applications include studying tumor metastasis and the growth of blood vessels that help feed a tumor. It could also help reveal how immune cells attack the body's organs in cases of autoimmune disease.
The research was funded by the National Institutes of Health, the New York Stem Cell Foundation, Jeremy and Joyce Wertheimer, the National Science Foundation, and the Fannie and John Hertz Foundation and was published in a recent edition of the journal Science.
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