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Nanoapertures to enhance single molecule fluorescence detection

Metal nanoapertures and zero-mode waveguides

Milling a nanometer-size aperture in a metallic film is an intuitive way to fabricate new nanophotonic devices that are robust and highly reproducible. Although the concept appears very simple, such apertures (also known as zero-mode waveguides) exhibit attractive properties for biophotonics :

  • localization of excitation light
  • strong isolation from emission produced by species located outside the aperture
  • enhancement in the fluorescence signal

Bright unidirectional fluorescence emission with corrugated apertures

To increase and control the light emitted by a single molecule, we use a special kind of nanoantenna made of an aperture surrounded by circular corrugations milled in a gold film. This antenna transforms a standard molecule into a bright unidirectional fluorescence source : the fluorescence intensity is enhanced up to 120 fold, and almost all the light is emitted into a narrow cone in the vertical direction. Both the emission intensity and direction can be controled down at the single molecule level, which realizes a major breakthrough.

Plasmonic Antennas for Directional Sorting of Fluorescence Emission

Despite intense recent research, tuning the directionality of fluorescence emission remains an open challenge for emitters with random positions and orientations, which bear a major role in biosensing. To solve this issue, we propose a class of corrugated aperture antennas to control the fluorescence emission directivity for molecules in solution. The key result is that for each emission wavelength the fluorescence beam can be directed along a specific direction with a given angular width.

Beaming of fluorescence light with plasmonic crystals

Collecting each and every photon that a single molecule emits is a major goal in nanophotonic devices. Small plasmonic crystals patterned in gold film result in strong directionality of emission for molecules located in the structure. This work pioneers the control of directionality by coherent coupling in finite antenna arrays driven by a single emitter. Moreover, it demonstrates that fluorescence radiation patterns can be designed at will by engineering surface plasmon Bloch modes. These results open a rich toolbox to engineer single photon emitters to emit selectively in particular angles, polarization states, or in more exotic beam profiles.

Selected publications

  • H. Aouani, O. Mahboub, N. Bonod, E. Devaux, E. Popov, H. Rigneault, T.W. Ebbesen, J. Wenger, Bright Unidirectional Fluorescence Emission of Molecules in a Nanoaperture with Plasmonic Corrugations, Nano Lett. 11, 637-644 (2011) PDF
  • H. Aouani, O. Mahboub, E. Devaux, H. Rigneault, T.W. Ebbesen, J. Wenger, Plasmonic antennas for directional sorting of fluorescence emission, Nano Lett. 11, 2400-2406 (2011).
  • Langguth L., Punj D., Wenger J., Koenderink F. Plasmonic Band Structure Controls Single-Molecule Fluorescence, ACS Nano 7, 8840-8848 (2013).
  • J Wenger, D Gerard, J Dintinger, O Mahboub, N Bonod, E Popov, T. W. Ebbesen, and H. Rigneault, Emission and excitation contributions to enhanced single molecule fluorescence by gold nanometric apertures, Opt. Express Vol. 16, pp.3008-3020 (2008) PDF