Graphene-Based Measurement Technique Boosts Optical Resolution

Researchers at the University of Göttingen have developed a new technique that exploits the unusual properties of graphene to optically measure extremely small distances — to the order of one ångström — for the first time. This could mean big things for superresolution microscopy.

“Our method has enormous potential for superresolution microscopy because it allows us to localize single molecules with nanometer resolution not only laterally, as with earlier methods, but also with similar accuracy along the third direction,” said Arindam Ghosh, a Ph.D. student at Göttingen and first author of the paper. “[This] enables true three-dimensional optical imaging on the length scale of macromolecules.”

Using the new method, the researchers have made it possible, for the first time, to optically measure what makes up the membranes of all living cells. Specifically, the researchers were able to measure the thickness of single lipid bilayers, which are composed of two layers of fatty acid chain molecules and have a total thickness of only a few nanometers.

On the left: Image of single molecules on the graphene sheet. Such images allow scientists to determine the position and orientation for each molecule. Comparison with the expected image (right) shows excellent agreement. Courtesy of the University of Göttingen.

In the study, a single, one-atom-thick graphene sheet was used to fine-tune the emission of fluorescent molecules when they came close to it. By depositing single molecules above the graphene layer, the researchers were able to determine their distance by monitoring and evaluating their light emission.

A dye-labeled membrane seen under polarized light (arrow). This shows that molecules are oriented along the perimeter of the membrane. Courtesy of the University of Göttingen.

“This will be a powerful tool with numerous applications to resolve distances with subnanometer accuracy in individual molecules, molecular complexes, or small cellular organelles,” said Göttingen physics professor Jörg Enderlein, head of the school’s Third Institute of Physics (Biophysics).

According to the researchers, this graphene-induced modulation of molecular light emission provides an extremely sensitive and precise “ruler” for determining single molecule positions in space. The new technique is so accurate that distance changes of even one ångström can be resolved.

The research was published in Nature Photonics (https://doi.org/10.1038/s41566-019-0510-7).