Physicists from UC Berkeley and Lawrence Berkeley National Laboratory have developed a laser-based phase plate for cryo-electron microscopy (cryo-EM) that improves imaging contrast for small biological structures. The technology, called Theia, expands the range of proteins and cellular features that researchers can study using cryo-EM, with potential implications for structural biology and advanced imaging workflows.
One of the core challenges in cryo-EM is imaging small proteins. To preserve delicate biological samples, researchers use low-intensity electron beams. While this approach helps maintain structural integrity, it can produce weak signals that are difficult to distinguish from background noise, particularly for smaller molecules.
Theia addresses this limitation by applying phase-contrast techniques to electron microscopy. The system uses a 75-kilowatt continuous laser trapped within a mirrored cavity to shift the phase of the electron beam by 90 degrees. This approach enhances image contrast without requiring chemical stains or increasing electron beam intensity.
Holger Müller, professor of physics at UC Berkeley, led the long-term development effort with a multidisciplinary team of physicists, engineers, microscopists, and machinists.
“Before, studying structures with cryo-EM was like trying to look at paintings in a dark gallery. With Theia, it's like the lights have been turned on for the first time,” said Müller.
Expanding cryo-EM capabilities
Cryo-EM enables researchers to visualize biological molecules in near-native states, but many small proteins remain difficult to resolve using conventional methods.
In testing, researchers found that the laser phase plate provided particularly strong improvements when imaging small particles and lower-quality specimens. Enhanced contrast improved the amount of structural information recovered from challenging samples and supported more robust computational reconstructions.
The team demonstrated the technology using hemoglobin, a widely studied protein that serves as a benchmark for cryo-EM performance. Improved imaging allowed researchers to generate more accurate structural models.
The researchers suggest the approach could eventually extend cryo-EM access to proteins that are currently near or beyond the practical limits of existing systems.
Potential applications in cryo-electron tomography
The team is also exploring applications in cryo-electron tomography (cryo-ET), which enables researchers to visualize biological structures within intact cells.
“In cryo-ET, the ability to look at cells in their native context is one of its main advantages,” said Jessie Zhang, a postdoctoral researcher at UC Berkeley. “However cells can be very messy, and the low signal to noise in conventional EM makes interpreting tomograms a challenge. The laser phase plate has the potential to allow biologists to see and understand more of the proteome in action.”
Improved contrast may help researchers distinguish cellular structures that are currently difficult to resolve, expanding the potential utility of cryo-ET in cellular biology.
Outlook for imaging facilities
Theia remains a specialized research instrument optimized for performance rather than routine laboratory deployment. Additional engineering and development will be required before similar systems become broadly available in commercial cryo-EM platforms.
For imaging facilities, the work reflects ongoing advances in electron microscopy and the continued expansion of structural biology capabilities. As new generations of cryo-EM tools emerge, laboratories may need to evaluate how these technologies align with research priorities, infrastructure needs, and long-term instrumentation planning.
The development underscores how advances in electron optics and contrast enhancement continue to broaden the types of biological questions that cryo-EM can address.
This article was created with the assistance of Generative AI and has undergone editorial review before publishing.
