A number of important biological processes, such as photosynthesis and vision, depend on light. But it’s hard to capture responses of biomolecules to light because they happen almost instantaneously.

Now, researchers have made a giant leap forward in taking snapshots of these ultrafast reactions in a bacterial light sensor. Using the world’s most powerful X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory, they were able to see atomic motions as fast as 100 quadrillionths of a second – 1,000 times faster than ever before.

“We’re the first to succeed in taking real-time snapshots of an ultrafast structure transition in a protein, in which a molecule excited by light relaxes by rearranging its structure in what is known as trans-to-cis isomerization,” says the study’s principal investigator, Marius Schmidt from the University of Wisconsin, Milwaukee.

The technique could benefit studies of light-driven, ultrafast atomic motions. For example, it could reveal:

  • How visual pigments in the human eye respond to light, and how absorbing too much of it damages them.
  • How photosynthetic organisms turn light into chemical energy – a process that could serve as a model for the development of new energy technologies.
  • How atomic structures respond to light pulses of different shape and duration – an important first step toward controlling chemical reactions with light.

“The new data show for the first time how the bacterial sensor reacts immediately after it absorbs light,” says Andy Aquila, a researcher at SLAC’s Linac Coherent Light Source, a DOE Office of Science User Facility. “The initial response, which is almost instantaneous, is absolutely crucial because it creates a ripple effect in the protein, setting the stage for its biological function. Only LCLS’s X-ray pulses are bright enough and short enough to capture biological processes on this ultrafast timescale.”