Introduction

This blog describes Jerome Wenger's research on Nano-Bio-Photonics.

Research interests: Nano-Optics, Biophotonics, Plasmonics, Single Molecules, Molecular Sensing & Spectroscopy

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Contact : jerome.wenger{-at-}fresnel.fr

Fresnel Institute CNRS UMR7249

Domaine Universitaire St Jerome

13397 Marseille, France

Phone: +33 4 91 28 84 94

twitterlogo.jpg Twitter profile: jeromewenger

 

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People involved

Current squad:

- Jerome Wenger (PI)

- Deep Punj (PhD)

- Juan de Torres (PhD)

- Victor Grigoriev (PostDoc)

- Petru Ghenuche (PostDoc)

- Satish Moparthi (PostDoc)

- Laetitia Le Guay (Staff)

 

Fresnel lab coworkers:

- Nicolas Bonod

- Patrick Ferrand

- Sophie Brasselet

- Herve Rigneault

 

Collaborations:

- Thomas Ebbesen / ISIS

- Steve Blair / Utah Univ.

- Dan Oron / Weizmann Inst.

- Niek Van Hulst / ICFO

- Maria Garcia Parajo / ICFO

- Romain Quidant / ICFO

- Femius Koenderink / AMOLF

- Sebastien Bidault / Langevin Inst.

- Jerome Plain / LNIO UTT

 

Former coworkers:

- Richard Hostein (PostDoc)

- Nadia Djaker (PostDoc)

- Davy Gerard (PostDoc)

- Benoit Cluzel (PostDoc)

(all now assistant professors)

- Heykel Aouani (PhD, now postdoc at Imperial College)

 

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Curriculum J. Wenger

2012: Habilitation à Diriger des Recherches

2011: ERC Starting Grant

2009: Promoted 1st class by CNRS

2005: CNRS researcher (Institut Fresnel, Marseille)

2004: PhD Quantum Optics (Institut d'Optique, Orsay)

2001: Engineer Institut d'Optique Graduate School (Orsay)

Born April 1978

 

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Mardi 15 avril 2014 2 15 /04 /Avr /2014 20:34

There is currently one opening position for an Attaché Temporaire d'Enseignement et de Recherche ATER (one-year non-renewable assistant professor contract) associated to Aix Marseille University. The research program will be done in one the groups at the Fresnel Institute under the supervision of a statutory researcher.

Deadline for application April 30th

Contract start September 1st

See the application procedure: http://drh.univ-amu.fr/public_content/recrutement-ater-2014-2015-modalites-liste-postes-section

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Jeudi 10 avril 2014 4 10 /04 /Avr /2014 14:36

Some new elements about the debate whether Förster resonance energy transfer can be tuned (or not) with the photonic environment have been recently published in Nature Communications.The authors use a model system of LaPO4 nanocrystals co-doped with Ce3+ donors and Tb3+ acceptors.To tune the photonic environment and the local density of optical states (LDOS), the authors change the refractive index n of the solvent. The experiments conclude that the donor emission rate increases linearly with the refractive index n, while the energy transfer rate does not.This brings the authors to the general conclusion that "FRET rates are independent of the photonic environment". I feel this conclusion so abrupt that it deserves at least a comment here.

First, let's look back at Förster theory as derived in the late 40s. On wikipedia, one can readily find that the rate of spontaneous emission can be described by Fermi's golden rule, and that under the dipole approximation the radiative rate is given by:

http://upload.wikimedia.org/math/0/8/2/08231fe0375d78aac590fb11cce58c94.png

which directly shows that the emission rate scales linearly with the refractive index n of the environment. This is what the authors observe for their donor emission. Turning to FRET, the well-established Förster theory states that the energy transfer rate scales as the product of the donor emission rate in absence of the acceptor time the sixth power of the Förster radius Ro, which is given by:

a022c35f4e4ebf96c1561aaddf11080c.png

Here, the Förster formalism indicates that Ro scales with the refractive index as (1/n4)1/6 so 1/n2/3, which is almost constant for most refractive indexes of common solvents. So the Förster radius is not expected to vary noticeably as the refractive index is changed, which is again what the authors observe.

The expected evolution of the energy transfer rate  ΓFRET = Γ rad (R0/r)6 can be deduced from the two equations above as function of the refractive index. The FRET rate then evolves as n/n4 = 1/n3, so the energy transfer rate actually decreases when the refractive index is increased. Nothing really special here, just the standard Förster theory from 1948.

Based on the above observations, how can one conclude that FRET rates are independent of the photonic environment? What is true (and well within the Förster theory) is that increasing the refractive index increases the radiative decay rate and reduces the energy transfer rate. However, the authors skip that the refractive index comes as some sort of prefactor in the porportionality relationship between the emission rate and the LDOS. There are actually two ways to tune the LDOS and the photonic environment. The obvious way is to change the medium refractive index (or the emission wavelength). The second (and physically relevant) way is to play with the secondary local field Es that is back-scattered by the (inhomogeneous) environment onto the emitter (equivalent to Green's dydadic approach). This is the only way to enhance the LDOS by more a hundred times, and requires photonic crystals or plasmonic antennas.

This is not simply a pure theory debate, FRET has huge applications in bioimaging, lighting sources and photovoltaics, and plays a key role in photosynthesis. Only complex photonic environments can assess the relationship of FRET with the LDOS and unlock the application of the nanophotonics toolbox to enhance FRET.

Do not get me wrong: I don't say/think the paper is wrong, I don't say/think the reviewers or editors took a bad decision, I don't go into personal debate. I simply discuss the scientific conclusion that one can draw from this study, they are far away from "settling the debate about conversion of light".

http://www.nature.com/ncomms/2014/140402/ncomms4610/images/ncomms4610-i1.jpg

Jeudi 10 avril 2014 4 10 /04 /Avr /2014 11:18

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.

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Mercredi 2 avril 2014 3 02 /04 /Avr /2014 22:33

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

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Mercredi 2 avril 2014 3 02 /04 /Avr /2014 22:24

We have recently published a review paper about plasmonic antennas and zero mode waveguides (nanoapertures) to enhance the detection and analysis of fluorescent molecules. Single molecule spectroscopy techniques, FRET and FCS can greatly benefit from zero mode waveguides and plasmonic antennas to enter a new dimension of molecular concentration reaching physiological conditions. You can find the review on WIREs Nanomedicine and Nanobiotechnology, or alternatively, we posted an unedited version on arXiv.

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