Researchers at the University of Göttingen (Göttingen, Germany) have developed a method that takes advantage of the unusual properties of graphene to electromagnetically interact with fluorescing (light-emitting) molecules. The method allows scientists to optically measure extremely small distances, on the order of 1 ångström (Å), with high accuracy and reproducibility. This enabled the researchers to optically measure the thickness of lipid bilayers, which make up the membranes of all living cells.
The research team, led by Jörg Enderlein, head of the Third Institute of Physics at the University of Göttingen and the corresponding author of the paper that describes the work, used a single sheet of one-atom-thick (0.34 nm) graphene to modulate the emission of fluorescent molecules when they came close to the graphene sheet. The excellent optical transparency of graphene and its capability to modulate the molecules' emission through space made it an extremely sensitive tool for measuring the distance of single molecules from the graphene sheet.
The method's accuracy can resolve even the slightest distance changes of around 1 Å—to demonstrate this, the scientists deposited single molecules above a graphene layer. They could then determine their distance by monitoring and evaluating their light emission. This graphene-induced modulation of molecular light emission provides an extremely sensitive and precise "ruler" for determining single molecule positions in space. They used this method to measure the thickness of single lipid bilayers, which are constituted of two layers of fatty acid chain molecules and have a total thickness of only a few nanometers.
"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, which enables true three-dimensional optical imaging on the length scale of macromolecules," says Arindam Ghosh, the first author of the paper.
"This will be a powerful tool with numerous applications to resolve distances with sub-nanometer accuracy in individual molecules, molecular complexes, or small cellular organelles," adds Enderlein.
Full details of the work appear in the journal Nature Photonics.