Mirage effect induced by optical antennas at the nanoscale

Antennas, like the ones employed in our radio appliances, can act as receivers and emitters of electromagnetic radiation with characteristic wavelengths in the meter range. These antennas have been extensively studied and are widespread in modern devices.

During the last decade, scientists have focused on the study of antennas which are approximately a billion times smaller than the typical antenna sticking out of our bathroom radio. These antennas are based on metallic nanostructures of different materials (such as for example gold) and different shapes (such as for example spheres). Furthermore, these antennas can also act as receivers and emitters of electromagnetic radiation but at much shorter wavelengths, in the sub-micrometer range covering the optical spectrum. These optical antennas are of great interest to control light at the nanoscale beyond common optical resolution.

Scientists at TU-Braunschweig directed by Prof. Philip Tinnefeld and junior research group leader Dr. Guillermo Acuna from the Institute for Physical Chemistry and the laboratory of emerging nanometrology (LENA) have performed novel contributions to the understanding of these optical antennas. To this end, they have employed the so-called DNA origami technique to place gold spherical nanoparticles next to fluorescent molecules. “This technique is in our lab indispensable” explains Prof. Tinnefeld. “It enables the positioning of different nanostructures with nanometer precision. It is like Lego, only a million times smaller. This allows countless new applications in nanotechnology.“

In order to study these structures, researchers employed super-resolution fluorescence microscopy, a technique that was awarded the Chemistry Nobel prize in 2014. This technique can determine the position of fluorescent molecules with 40 times more precision than conventional optical microscopes. If a metallic nanoparticle is placed close to a fluorescent molecule, the nanoparticle acts like an antenna and mediates the light emission from the fluorescent molecule. Therefore, the location of the molecule seems to be shifted from its actual position where the molecule is placed: a mirage effect on the nanoscale (see figure). This effect could be finally shown and quantitatively measured by the Braunschweig group.

„This type of projects has a huge impact for the Braunschweig research network”, said Mario Raab, first author of the publication and member of the Lena graduate school NanoMet. “LENA as well as NanoMet have clear research goals to further develop nanotechnology and associated measurement techniques. In this work we have realized both these objectives. In follow up developments, we will work in close cooperation with our important networking partner, the National Metrology Institute (PTB).”

The project emerged from an international cooperation with Prof. Fernando Stefani (Buenos Aires) who inspired the team during a Mercator Fellow research stay in Braunschweig. The experience of Prof. Tinnefeld and Dr. Guillermo Acuna in several research fields, a unique combination of DNA nanotechnology, super-resolution microscopy and plasmonics was decisive for the realization of the project and publication in a high ranked journal such as Nature Communications. The research was supported an ERC starting grant of the European Union, the German research foundation DFG and the Wissenschaftsallianz Braunschweig-Hannover (Forschungslinie Quanomet).



Figure Sketch of DNA origami structures (left) with three fluorescent molecules (red) with and without a gold nanoparticle (yellow) and the corresponding super-resolution images (right). The presence of the nanoparticle shifts the localization of the center fluorescent molecule



Mario Raab, Carolin Vietz, Fernando Daniel Stefani, Guillermo Pedro Acuna & Philip Tinnefeld
Shifting molecular localization by plasmonic coupling in a single-molecule mirage




Dr. Guillermo Acuna and Prof. Philip Tinnefeld
Institute for Physical and Theoretical Chemistry and
Laboratory for Emerging Nanometrology
Technische Universität Braunschweig
Hans Sommer Str. 10
D-38106 Braunschweig


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