Optical biosensors usually operate via energy transfer: The target molecule binds to the sensor complex. Consequently, the complex changes its shape so that two fluorescence molecules attached come closer together. As a result the one on the higher energetic level transfers energy to the other one and both their fluorescence radiation changes. Either the emitted wavelength or the signal strength changes - depending on the kind of biosensor.
The group of Prof. Philip Tinnefeld (E-Conversion / LMU München) and Dr. Izabela Kaminska from the Polish Academy of Science now answered a question that is crucial for the quality of biosensors: What is the perfect distance between energy donor and acceptor for getting the optimal energy transfer and thereby the best signal? For this purpose, they designed a special experimental set-up and applied two elements that are quite unusual for biosensors: graphene and DNA.
The perfect distance
Graphene is an excellent energy acceptor and for this reason can substitute the second fluorescence molecule within the experiment. Having a two-dimensional structure, it also builds the surface on which the scientists install the other fluorescence molecule. They put it on a kind of pillar that they designed out of DNA using the so-called DNA origami method. It allows to define the pillar length with nanometer precision. On the pillar, the distance between the first fluorescence molecule and the graphene was tuned exactly. The experiment shows a clear winner: With a distance of 18 nanometers, the signal strength changes the most.
An unusual couple
The combination of graphene and DNA is quite unusual. Hence finding the perfect “glue” was at the top of the scientists´ list. The aromatic molecule pyrene proved to be an invaluable find. Its cyclic structure is similar to graphene and at the same time can be attached to DNA. Both materials are not only attractive because of their high conductivity and the characteristic as defined spacers. They also exhibit features that might be interesting for the design of new biosensors: Graphene is translucent due to its one-atom thickness and at the same time extremely stable. In addition, DNA structures are highly compatible and versatile for docking complex biosensing systems.
Therefore, the findings of the teams from Munich and Warsaw clearly call for numerous new ideas and projects.
Distance Dependence of Single-Molecule Energy Transfer to Graphene Measured with DNA Origami Nanopositioners, I. Kaminska, J. Bohlen, S. Rocchetti, F. Selbach, G.P. Acuna, P. Tinnefeld, Nano Letters, 19 (7), pp. 4257-4262, 2019