Laser Phase Plate Breakthrough Extends Cryo-EM to Smaller Proteins, Opening New Frontiers in Structural Biology

A team of physicists at the University of California, Berkeley, and Lawrence Berkeley National Laboratory (search)Search term has developed a laser-based phase plate for cryo-electron microscopy that dramatically improves the imaging of small proteins—molecules that have long remained beyond the reach of even the most powerful biological microscopes. The advance, published June 11, 2026 in Science, adapts a nearly century-old optical technique to modern cryo-EM and could reshape how researchers study the molecular underpinnings of disease.

The innovation centers on an exceptionally intense focused continuous-wave laser that alters the phase of an electron beam without significantly reducing its intensity. By shifting the phase of unscattered electrons, the system converts nearly invisible differences in biological specimens into detectable changes in brightness—allowing proteins once thought too small to resolve to come into view.

“Cryo-EM has become the new, fastest-growing method for resolving the structure of biological macromolecules, and cryo-ET is expected to show how these molecules work together in their natural, cellular context,” said Holger Müller, a UC Berkeley (search)Search term professor of physics and faculty scientist at Lawrence Berkeley National Laboratory (search)Search term who led the development effort. “But because of signal-to-noise limitations, the majority of human and animal proteins are too small to be analyzed by these methods. The increase in signal-to-noise ratio provided by this laser phase plate is expected to overcome these important limitations.”

A 15-Year Effort Comes to Fruition

Phase contrast was first developed by Dutch physicist Frits Zernike in 1930, earning him the 1953 Nobel Prize in Physics. The method revealed transparent cellular structures under light microscopes without staining, but early attempts to apply the same principle to electron microscopes faltered—phase plates weakened the beam, reduced resolution, or produced unstable images.

In 2010, Müller and cryo-EM pioneer Robert Glaeser proposed using an intense laser instead. It took 15 years of theoretical and experimental work to turn the concept into a functioning instrument. The team trapped a laser inside a spherical mirrored cavity where light reflects more than 10,000 times, concentrating into a tiny area.

“It’s 75 kilowatts focused to a few microns,” Müller said. “That’s more powerful than what you use for welding. It’s more power than a military laser. It builds up the brightest continuous laser focus ever.”

Pushing Beyond the 70-Kilodalton Barrier

Current cryo-EM instruments struggle to resolve proteins smaller than approximately 70 kilodaltons—yet proteins below that size account for roughly 90 percent of the human proteome. With the laser phase plate, researchers can now image proteins as small as 50 kilodaltons, and Müller hopes future refinements will lower that limit to 17 kilodaltons, the size of myoglobin (search)Search target.

The team tested the system on six biological samples. Aldolase (search)Search target, a muscle protein that cryo-EM can already image relatively well, showed improvement. But hemoglobinView drug details—a smaller oxygen-carrying protein near the lower size limit of current instruments and often used as a benchmark—benefited far more.

“For the most challenging cases—small particles, bad specimens—the laser produces a very considerable advantage,” Müller said.

Theia: A Custom-Built Platform

Biohub (search)Search term, a research collaborative in Redwood City, California, funded a customized Thermo Fisher Krios microscope that Müller equipped with the laser phase plate. He named the instrument Theia, after the ancient Greek Titaness associated with light. A second microscope under development at Biohub will use two perpendicular lasers at lower power to reduce optical distortions and protect components.

“Theia is the Formula 1 of microscopes,” Müller said. “It has extra electron optics that give it better resolution than the standard cryo-EM, even without the laser. With the addition of the laser phase plate, we hope that it really becomes the world’s best instrument overall.”

Toward Cryo-Electron Tomography

The system is currently installed at UC Berkeley (search)Search term, and the team is working to expand its capabilities beyond single-particle analysis to cryo-electron tomography (cryo-ET). Much like CT scans in a hospital, cryo-ET assembles different angular views into a three-dimensional image—but captures molecules in their natural states inside cells, offering far higher resolution than light microscopy.

“With cryo-ET, we’re looking at small, very complicated cellular material that’s incredibly crowded inside the cell,” said Bridget Carragher, founding technical director of imaging at Biohub (search)Search term. “It’s like a forest of trees, and you’re trying to find one leaf on one tree in there. Cryo-ET needs a dramatic step forward in contrast, so we can start to see what’s going on inside the cell. That’s what the laser phase plate promises to give us.”

Stephani Otte, Biohub (search)Search term’s Vice President of Imaging Science, underscored the broader implications: “This technology is a step function change for biology. We are going to be able to see how molecular machines operate inside the living cell, in context, for the first time. What was once invisible will become visible—and that changes everything about how we understand disease.”

The research was published under the title “Laser phase plate improves structure determination of small proteins by cryo-EM” with authors including Petar N. Petrov, Jessie T. Zhang, Jonathan Remis, Jeremy J. Axelrod, Hang Cheng, Eric S. Cooper, Ian K. Hicklin, Shahar Sandhaus, Cooper Schnurr, Robert M. Glaeser, and Holger Müller.