Nanoantennas Amplify Visible Light
Just as radio antennas amplify the RF signals of our mobile phones and televisions, the same principle can apply to light. For the first time, researchers from Centre national de la recherche scientifique (CNRS) and Aix Marseille Université have succeeded in producing a nanoantenna from short strands of DNA, two gold nanoparticles and a small fluorescent molecule that captures and emits light. This easy-to-handle optical antenna is described in an article published in the July 17, 2012 issue of Nature Communications. This work could, in the longer term, lead to the development of more efficient LEDs.
Because light is a wave, it should be possible to develop optical antennas capable of amplifying light signals in the same way as our televisions and mobile phones capture radio waves. However, because light oscillates a million times faster than radio waves, extremely small nanometer-sized objects are needed to capture such very rapid light waves. Consequently, the optical equivalent of an elementary antenna (of dipole type) would be a quantum emitter surrounded by two particles a thousand times smaller than a human hair.
For the first time, researchers from the Institut Langevin (CNRS / ESPCI Paris Tech / UPMC / Université Paris Diderot) in Paris and the Institut Fresnel (CNRS / Aix-Marseille Université / Ecole Centrale de Marseille) in Marseilles have developed such a bio-inspired light nanoantenna, which is simple and easy to handle. The processes are described in “Accelerated single photon emission from dye molecule driven nanoantennas assembled on DNA” by Mickaël P. Busson, Brice Rolly, Brian Stout, Nicolas Bonod and Sébastien Bidault; the full text and illustrations are available online.
They grafted gold particles (36 nm diameter) and a fluorescent organic colorant onto short synthetic DNA strands (10 to 15 nm long). The fluorescent molecule acts as a quantum source, supplying the antenna with photons, while the gold nanoparticles amplify the interaction between the emitter and the light. The scientists produced in parallel several billion copies of these pairs of particles (in solution) by controlling the position of the fluorescent molecule with nanometric precision, thanks to the DNA backbone. These characteristics go well beyond the possibilities offered by conventional lithography techniques currently used in the design of microprocessors. In the longer term, such miniaturization could allow the development not just of more efficient LEDs, but also faster detectors and more compact solar cells. These nanosources of light could also be used in quantum cryptography.