Forget super microscopes, MIT’s tissue expansion makes nanoscale imaging affordable

A classical way to image nanoscale structures in cells is with high-powered, expensive super-resolution microscopes.

As an alternative, MIT researchers have developed a way to expand tissue before imaging it — a technique that allows them to achieve nanoscale resolution with a conventional light microscope.

In the newest version of this technique, the researchers have made it possible to expand tissue 20-fold in a single step.

This simple, inexpensive method could allow nearly any biology lab to perform nanoscale imaging.

Can see inside tissues

At the resolution achieved by this technique, which is around 20 nanometers, scientists can see organelles inside cells and clusters of proteins.

With a 20-fold expansion, researchers can use a conventional light microscope to resolve about 20 nanometers.

This allows them to see cell structures like microtubules and mitochondria, as well as clusters of proteins.

In the new study, the researchers set out to perform a 20-fold expansion with only a single step.

This meant that they had to find a gel that was both extremely absorbent and mechanically stable so that it wouldn’t fall apart when expanded 20-fold.

They used a gel assembled from N, N-dimethyl acrylamide (DMAA), and sodium acrylate to achieve that.

Unlike previous expansion gels that rely on adding another molecule to form crosslinks between the polymer strands, this gel forms crosslinks spontaneously and exhibits strong mechanical properties.

Such gel components previously had been used in expansion microscopy protocols, but the resulting gels could expand only about tenfold.

The MIT team optimized the gel and the polymerization process to make the gel more robust and allow for a 20-fold expansion.

To further stabilize the gel and enhance its reproducibility, the researchers removed oxygen from the polymer solution before gelation, preventing side reactions that interfere with crosslinking.

This step requires running nitrogen gas through the polymer solution, which replaces most of the oxygen in the system.

Once the gel is formed, select bonds in the proteins that hold the tissue together are broken, and water is added to expand the gel. After the expansion, target proteins in tissue can be labeled and imaged.

Imaging tiny structures

Using this technique, the researchers could image many tiny structures within brain cells, including synaptic nanocolumns.

These are clusters of proteins arranged in a specific way at neuronal synapses, allowing neurons to communicate with each other via the secretion of neurotransmitters such as dopamine.

In studies of cancer cells, the researchers also imaged microtubules — hollow tubes that help give cells their structure and play important roles in cell division.

They could also see mitochondria (organelles that generate energy) and even the organization of individual nuclear pore complexes (clusters of proteins that control access to the cell nucleus).

The researchers are now using this technique to image carbohydrates known as glycans found on cell surfaces and help control cells’ interactions with their environment.

This method could also be used to image tumor cells, allowing scientists to glimpse how proteins are organized within those cells much more easily than possible.

The researchers envision that any biology lab should be able to use this technique at a low cost since it relies on standard, off-the-shelf chemicals and common equipment such as confocal microscopes and glove bags, which most labs already have or can easily access.