Color highlights detail in electron microscope images

On the left is a standard grayscale electron micrograph of a mouse brain, and on the right is a Multicolor image of the same area, that better highlights the different structures and their relationship(Credit: Stephen Adams, NCMIR, UC San Diego)

Electron microscopes (EM) are useful for creating a topographical map of cellular structures and molecules, but since the images are obtained with particle beams of accelerated electrons, the results are only rendered in grayscale, and colored artificially after the fact. But researchers have now developed a new method for producing electron micrographs with several colors, highlighting different components and details that normally wouldn't be visible.

Like those colored in post production, the team's new multicolor EM images don't display true color, but the technique allows for a more dynamic view of the microscopic landscape and helps scientists identify different components, and how they interact.

To create them, the team sequentially painted different cellular structures with precipitates of rare earth metals like lanthanum, cerium and praseodymium, which allows the electron microscope to differentiate between them. Then it's a matter of adding color based on those cues.

"A transmission electron microscope can distinguish each of these metals by electron energy-loss to give elemental maps of each that can be overlaid in color on the familiar monochrome electron micrograph," says Stephen R. Adams, first author of the study. "Each color highlights a different component of the cellular ultrastructure."

Normally, electron microscopy labels structures with gold particles, but they tend to show up as nondescript black spots. This coloring technique brings an improved level of detail to the images, along with a higher spatial resolution than using fluorescence microscopy.

"The ability to discern multiple specific molecules simultaneously adds a new dimension," says Mark H. Ellisman, co-senior author of the study. "It reveals details, actions and processes that aren't necessarily visible — or even suspected — in a more monochromatic view."

While these multicolor EM images can only display in two colors for the moment, the team believes that the palette can be widened by developing new ways to precipitate more lanthanides, increasing the number of different structures the system can identify. With or without the extra colors, the technique is useful and simple enough to be rolled out to other facilities.

"The method is quite simple to do, uses easily made chemicals and requires detectors that are already present on many transmission electron microscopes so it is potentially readily transferable to other laboratories," says Adams. "Further research is needed to improve the chemistry and sensitivity of the method, but this work will hopefully inspire other groups to devise similar methods in this field."

The research was a collaboration between scientists at the University of California San Diego School of Medicine and Howard Hughes Medical Institute, and the study was published in the journal Cell Chemical Biology.

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