Microscopy method improved to bring fine details into view

"This is a radically new way of doing microscopy," said UW chemistry professor Joshua Vaughan, who is senior author on a paper detailing their approach in Nature Methods. "The focus had largely been on hardware—improving the resolution of microscopes. Here, we expand the cell's interior to bring it into view."

Appropriately, this technique is known as expansion microscopy. "This is a simple and robust approach that is surprisingly effective," added Vaughan.

His team was inspired by the expansion approach developed at the Massachusetts Institute of Technology. The MIT researchers stained cells with a complex, DNA-based fluorescent probe that would make cellular contents visible.

They then treated cells with an expandable polymer that linked to the custom probes and would "inflate" the specimens to as much as four times their original size. But, this approach was laborious, and required specialised, expensive reagents.

"When I saw their approach, I thought it was amazing," said Vaughan. "But we were wondering if there was a way to do this using simpler staining strategies and conventional probes. That would make expansion microscopy accessible to thousands of labs."

Instead of complex fluorescent probes, Vaughan's team turned to conventional fluorescent dyes bound to antibodies, which are easier to use, and developed a simple chemical treatment that would allow the antibodies to become linked to the polymer.

They then treated their stained samples—slices of mammalian brain tissue and cultured cells—with the expandable polymer as well as enzymes that could create small "snips" in proteins to help them expand.

They used this basic approach to come up with two staining protocols for expansion microscopy—one that worked better for individual cells and another for slices of tissue. Under the microscope, their images showed substantially brighter stains while maintaining excellent resolution.

As an added bonus, their approach also enables expansion microscopy with fluorescent proteins, another popular fluorescent probe used by biologists. Critically, the UW team was able to obtain these high-resolution images on conventional, widely used laboratory microscopes.

"We think this will make expansion microscopy a widely used technique for researchers who want to visualise what they're studying with a relatively simple, low-cost approach that also has excellent performance," said Vaughan.

Vaughan said he hopes that other research groups will modify his team's basic approach for other organisms or cell types, especially structures like cell walls that would resist expansion.