A new way to image organic compounds that eliminates the need to freeze specimens has been devised by researchers at the Okinawa Institute of Science and Technology Graduate University (OIST). By suspending organic samples in water vapor, OIST scientists found they could keep samples in their native, wet state and still allow for ultrahigh resolution imaging.
Their study, published in PLOS ONE last month, could simplify what is currently a time-consuming and difficult process.
Usually, in order to view samples—particularly, fragile organic samples—inside a high-powered transmission electron microscope, scientists must undertake extensive preparation. Creating a plate of ice a fraction of a nanometer thick with a particular crystal structure can require many trials. This labor-intensive process, which can take months, inspired Cathal Cassidy, lead author on the paper and a researcher at OIST's Quantum Wave Microscopy Unit, to try another method.
The team first used gold to demonstrate that atoms can be successfully imaged inside water vapor. Then, they looked at a virus using the same method. The sample remained stable, and the resulting image came out crisp, in relatively high resolution.
The method devised by OIST researchers provides a feasible alternative to current approaches. The sample, which is suspended in water vapor, is pumped into the portion of the tube surrounding the sample and rapidly pumped out again. Tiny apertures above and below the sample allow the electron beam to pass directly through it. Because the sample is not enclosed by ice or glass, it can be tilted for three-dimensional imaging.
Cassidy emphasized that the study is a first step toward high-resolution imaging of hydrated samples in water vapor. He said he hoped biologists would build on the results.
"Anybody who wants to try it or play with it, they can do it," he said, pointing to the availability of data. "If somebody else takes the baton and pushes this forward, I'd be really happy with that."
Image: Scientists imaged gold nanocrystals (shown here in false-color) using a 300kV electron beam, through 1.3kPa of water vapor. Image courtesy of OIST.