Cellular processes often unfold in the blink of an eye — a surge of calcium ions, a rapid contraction of a heart muscle cell. Capturing these transient events in detail has long challenged modern microscopy: the faster the observation, the blurrier the image. 

An international team led by Osaka University has now presented a breakthrough method that overcomes this limitation: time-deterministic cryo-optical microscopy. The technique allows researchers to freeze living cells during observation under the microscope within milliseconds, creating a high-resolution, quantitatively accurate snapshot of dynamic cellular activity. The findings have been published in Light: Science & Applications. 

Contribution from Jena: 3D reconstruction software enables spatial insight 

Professor Rainer Heintzmann of the Leibniz Institute of Photonic Technology (Leibniz IPHT) and Friedrich Schiller University Jena contributed his expertise in structured illumination microscopy (SIM) — a method in which a fine light pattern is projected onto the specimen. From these patterned images, optical sections can be reconstructed, enabling three-dimensional, super-resolved visualizations of cellular structures. 

To analyze the data obtained with this novel cryo-technique, Heintzmann provided a 3D reconstruction software developed at Leibniz IPHT. The software transforms raw microscopy data into detailed 3D images that reveal cellular structures and molecular processes with exceptional clarity. During a research stay in Osaka, Heintzmann also supported the team directly in the data analysis. 

“Combining our reconstruction software with this new cryo-based approach opens fascinating insights into cellular processes that were previously blurred or invisible,” says Rainer Heintzmann. 

Freezing fast cellular activity in time 

Using the new technique, the researchers succeeded in freezing the propagation of calcium ion waves in heart muscle cells. These frozen wavefronts could then be observed in three dimensions using super-resolution methods that normally cannot capture such rapid dynamics due to their slower acquisition speed. The system’s precision allows researchers to arrest biological processes within 10 milliseconds, offering an unprecedented level of temporal accuracy. 

This method bridges the gap between live-cell imaging and cryo-fixation, combining the advantages of both: dynamic biological events can be arrested in their native state, and then examined with multiple high-resolution optical microscopy techniques — such as super-resolution fluorescence and Raman microscopy — all aligned to the exact same moment in time. 

Perspectives for life sciences and biomedicine 

By providing temporally and spatially resolved “freeze frames” of fast biological events, time-deterministic cryo-optical microscopy opens up new avenues for studying the mechanisms behind heart rhythm disorders, neuronal signaling, or drug interactions at the molecular level. 

 

Image: On-stage freezing chamber, Cryofixation of cellular dynamics under microscopic observation, and cryogenic super-resolution imaging. Light: Science & Applications (Light Sci Appl)

Original Publication: Tsuji, K., Yamanaka, M., Kumamoto, Y. et al. Time-deterministic cryo-optical microscopy. Light: Science & Applications 14, 275 (2025). https://doi.org/10.1038/s41377-025-01941-8