recent research work

Our article “Multi-focus parallel detection of fluorescent molecules at picomolar concentration with photonic nanojets arrays” has just been released in Applied Physics Letters. We replace the complex microscope objective commonly used in fluorescence sensing by an array of latex microspheres. This realizes a novel regime where several focal spots are illuminated to detect the possible presence of a fluorescent molecule in one of them. A detailed theoretical description of the phenomen is provided along with experimental demonstration.
This work describes an efficient disposable lens element that enables single molecule sensitivity at low picomolar concentration. The simplicity of the design makes it perfect for integration in portable microfluidic readers.

Energy transfer between molecules is promoted when they are set in an environment that confines light

The energy transfer between molecules is an essential phenomenon for photosynthesis, photovoltaics and biotechnology. Now, thanks to the work of the Institut Fresnel Institute, energy transfer between molecules can be controlled and enhanced with optical structures etched at the nanoscale.

Researchers prepared pairs of energy donor and acceptor molecules linked by rigid double stranded DNA. These pairs were then inserted into apertures milled in a gold film with nanoscale dimensions. By accurately measuring the radiation properties of pairs of molecules, the researchers were able to demonstrate that the rate of energy transfer between molecules is 6 times greater when placed in a nanoaperture.

These promising results are clearing a new path to improve the energy transfer process widely used in life sciences and biotechnology. Optical nanostructures open up many potential applications for biosensors, light sources or photovoltaics.
This work has been supported by the European Research Council under ERC Grant 278242.

The ability to design metamaterials with the prescribed properties is a key to their numerous applications and a focus of intense studies in the photonics community. As metamaterials are engineered at a scale which is much smaller than the wavelength of light, it is possible to treat them as a homogeneous medium with the effective values of permittivity and permeability. Nevertheless, there is no common approach to extract these effective parameters despite the significant efforts of the research community over the last years.

In a recent paper published in Phys Rev B, we propose a novel approach to extract the homogenized parameters by analyzing the reflection and transmission spectra. We show that this generalization preserves the physical meaning of the effective parameters at high frequencies and in the vicinity of resonances, where the nonlocal contributions cannot be neglected. It is also shown the decomposition of scattering spectra into even and odd modes helps to separate various contributions and to derive the explicit formulas for the effective permittivity and permeability which always satisfy the passivity and causality constraints.

See our new preprint released on ArXiv 1403.2222: Nanophotonic enhancement of the Förster resonance energy transfer rate on single DNA molecules

Nanophotonics achieves accurate control over the luminescence properties of a single quantum emitter by tailoring the light-matter interaction at the nanoscale and modifying the local density of optical states (LDOS). This paradigm could also benefit to Förster resonance energy transfer (FRET) by enhancing the near-field electromagnetic interaction between two fluorescent emitters. Despite the wide applications of FRET in nanosciences, using nanophotonics to enhance FRET remains a debated and complex challenge. Here, we demonstrate enhanced energy transfer within single donor-acceptor fluorophore pairs confined in gold nanoapertures. Experiments monitoring both the donor and the acceptor emission photodynamics at the single molecule level clearly establish a linear dependence of the FRET rate on the LDOS in nanoapertures. These findings are applied to enhance the FRET rate in nanoapertures up to six times, demonstrating that nanophotonics can be used to intensify the near-field energy transfer and improve the biophotonic applications of FRET.

Jerome will attend SPIE Photonics Europe 2014 conference in Brussels on April 14-17. He will present four contributions from the group:

• Paper 9126-57 Plasmonic nanoantennas for enhanced single molecule analysis at high concentrations (invited paper)
• Paper 9126-62 Enhanced fluorescence emission from resonant DNA assembled plasmonic nanoantennas loaded with single dye molecules
• Paper 9129-91 Hollow core photonic crystal fiber probes for Raman and fluorescence spectroscopy with photonic nanojet focusing
• Paper 9125-62 Homogenization of metamaterials through the singular analysis of scattering spectra