CHICAGO-University of Michigan (UM) researchers have developed a powerful microscope that can map how light energy migrates in photosynthetic bacteria on timescales of one-quadrillionth of a second.

To develop the microscope, UM researchers use a method called two-dimensional electronic spectroscopy to generate images of energy migration within proteins during photosynthesis.

The instrument combines this method with a microscope to measure a signal from nearly a million times smaller volumes than before.

"We've now combined both of those techniques so we can get at really fast processes as well as really detailed information about how these molecules are interacting," said Jennifer Ogilvie, UM professor of physics and biophysics. In developing the microscope, Ogilvie and her team studied colonies of photosynthetic purple bacterial cells. By looking at an intact cell system, the researchers were able to observe how a complete system's different components interacted. They also studied bacteria that had been grown in high light conditions, low light conditions and a mixture of both. By tracking light emitted from the bacteria, the microscope enabled them to view how the energy level structure and flow of energy through the system changed depending on the bacteria's light conditions.

The microscope can help scientists understand how organic photovoltaic materials work. Instead of the light-harvesting antennae complexes found in plants and bacteria, organic photovoltaic materials have what are called "donor" molecules and "acceptor" molecules. When light travels through these materials, the donor molecule sends electrons to acceptor molecules, generating electricity.

"We might find there are regions where the excitation doesn't produce a charge that can be harvested, and then we might find regions where it works really well," Ogilvie said. "If we look at the interactions between these components, we might be able to correlate the material's morphology with what's working well and what isn't."

In organisms, these zones occur because one area of the organism might not be receiving as much light as another area, and therefore is packed with light-harvesting antennae and few reaction centers. Other areas might be flooded with light, and bacteria may have fewer antennae but more reaction centers. In photovoltaic material, the distribution of donor and receptor molecules may change depending on the material's morphology. This could affect the material's efficiency in converting light into electricity.

The study has been published in Nature Communications.