A ‘Ruler' For Molecules

Göttingen researchers are developing graphene methods that provide tenfold improved optical resolution

Researchers at the University of Göttingen have developed a new method that uses the special properties of graphene to interact electromagnetically with fluorescent (light-emitting) molecules. For the first time ever, scientists can accurately and reproducibly optically measure extremely small distances of the order of 1 Angstrom (the ten millionth part of a millimeter). The team thus determined the thickness of lipid bilayers, the substance that forms the membranes of living cells. The results were published in the journal Nature Photonics.

The research team of the University of Göttingen under the direction of Prof. Dr. med. Jörg Enderlein used a single graphene sheet, only one atomic layer thick (0.34 nm), to vary the emission of light-emitting (fluorescent) molecules as they approached the graphene sheet. The excellent optical transparency of graphene and its ability to affect the emission of molecules through space made it an extremely sensitive tool for measuring the distance of individual molecules from the graphene sheet. The method is so accurate that even the smallest changes in the distance of about 1 Angstrom (that is about the diameter of an atom or half a millionth of a human hair) can be resolved. The scientists were able to demonstrate this by depositing individual molecules over a graphene layer. They were then able to determine their distance by measuring and evaluating their light emission. This approach provides a highly sensitive and precise "ruler" for determining single molecular positions in space, which measures the thickness of individual lipid bilayers consisting of two layers of fatty acid chain molecules with a total thickness of only a few nanometers.

"Our method has tremendous potential for super-resolution microscopy because it allows us to localize single nanometer-resolution molecules along the third direction not only laterally, but also with similar accuracy, providing true three-dimensional optical imaging along the length scale of Allows macromolecules, "says Arindam Ghosh, lead author of the study.

"This will be a powerful tool with numerous applications to resolve distances of sub-nanometer accuracy in single molecules, molecular complexes or small cellular organelles," adds Enderlein, corresponding author and director of the Third Physics Institute (Biophysics), at which Work was done.