Ultrafast camera gives new view of molecular dynamics

13 Jun 2023

Japan project boosts time resolution to investigate details of cancer metastasis.

Better sensitivity: amplifier architecture

A project at Kyoto University and Okinawa Institute of Science and Technology (OIST) in Japan has developed what is said to be the world’s fastest camera for detecting fluorescence from single molecules.

The goal was to achieve high frame rates and photon sensitivity simultaneously, a balance that is particularly important for high-speed imaging of molecular dynamics in cells.

Reported in Journal of Cell Biology, the new camera could now be put to use for single fluorescent-molecule imaging (SFMI), in which a fluorescent molecule acts as a tag bound to other molecules of interest, revealing the complexities of cellular processes.

"Our work with this camera will help scientists understand how cancer spreads and help develop new drugs for treating it,” said Takahiro Fujiwara who led the research at Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS).

The camera architecture was designed around a microchannel-plate image intensifier and a high-speed CMOS sensor, coupled together via an optical fiber bundle. The fiber bundling enhances the signal reaching the sensor by a factor of 5 to 10 compared with lens coupling approaches taken in other cameras, according to the project.

The team opted for a conventional CMOS sensor rather than the scientific CMOS (sCMOS) version of the semiconductor technology because of the higher frame rates it can achieve, despite sCMOS generally offering lower readout noise and being more commonly used in fluorescence microscopy.

This involved careful design of the camera architecture, with an amplifier incorporated before the noisy detector. Ensuring that background noise from the detection of fluorescence was amplified to a level comparable to the readout noise of the CMOS sensor means that the detector's own behavior is no longer a disproportionately limiting factor. Calculations incorporating this deliberate "amplifier gain" can ultimately enhance the sensitivity of the overall system.

In trials, the project's camera registered single molecule movements that are 1,000 times faster than the normal video frame rate, according to the project's results. It detected a molecule with an attached fluorescent tag every 33 microseconds with 34 nanometre precision in position, or every 100 microseconds at 20 nanometre precision.

The ultimate rate possible with current fluorescent molecules

The camera was used in particular to improve the performance of PALM super-resolution methods, one of the family of enhanced resolution techniques awarded the Nobel Prize for chemistry in 2014. PALM allows the positions of individual molecules to be recorded down to around 20 nanometers, but can take 10 minutes to obtain an image, noted the project team.

With the new ultrafast camera the imaging process can be speeded up by a factor of 60, generating images of live cells in around ten seconds instead.

"The ultrahigh-speed camera system developed in this study has enabled the fastest SFMI ever performed," commented the project in its published paper. "This would represent the ultimate rate possible with the currently available fluorescent molecules."

The system could be particularly valuable for cancer studies. In a separate study the project used it to examine a cellular structure called the focal adhesion, a protein complex connecting internal cell constituents to the extracellular matrix outside, known to play a role in how cancer cells move and metastasize.

"In one investigation we found that a cancer-promoting receptor that binds to signalling molecules is confined within a specific cellular compartment for a longer time when it is activated," said Akihiro Kusumi from OIST. "In another, we revealed ultrafine structures and molecular movements within the focal adhesion that are involved in cancer cell activities."

Development of drugs that can interfere with the role of focal adhesions in cancer is a focus of worldwide research, and the new camera should assist these efforts by revealing details of how these structures move and interact with other structures inside and outside of cells.