recent research work

In a collaboration between the Fresnel Institute and ICFO-the Institute for Photonic Sciences, we report in Nature Nanotechnology a novel “antenna-in-box” platform for single molecule fluorescence detection with unprecedented resolutions and sensitivity. The innovative approach combines a plasmonic gap antenna for ultra-high fluorescence enhancement with a metal nanoaperture for optimized background-free operation. It allows for 1100-fold fluorescence brightness enhancement together with detection volumes down to 58 zeptoliters (1 zL = 1e-21L), realizing a gain of four orders of magnitude as compared to classical microscopes. The antenna-in-box offers a highly efficient platform for nanoscale biochemical assays with single molecule sensitivity at physiological conditions.

Read our press release here, and the article in Nature Nanotechnology.

Deep's abstract on Plasmonic nanoantennas for enhanced single molecule analysis at micromolar conentrations has just been promoted for invited talk presentation at the 6th International Conference on Surface Plasmon Photonics SPP6.

As a teaser, our main claims are:

• fluorescence enhancement up to 1100-fold AND fluorescence brightness per molecule up to 400kHz (detected)
• detection volume measured down to 58 zeptoliters, four orders of magnitude below the diffraction limit
• true single molecule detection above 20 µM concentration actually measured
• our dedicated design is fully compatible with detection of single fluorescent molecules in solution and fluorescence correlation spectroscopy

The development of bright water-soluble luminescent probes is a ubiquitous problem in imaging and sensing applications. Designing fluorescent dyes typically relies on a molecular engineering approach in which photophysical properties are tuned by chemical modifications. In a letter published in Angewandte Chemie, we present a novel way of engineering luminescence by changing the photonic environment of a chromophore while maintaining its solubility. This has remained a challenge since the pioneering of this field in the 1970s, mainly because the photonic approach requires combining, in a single hybrid nanostructure, a luminescent molecule and an optical cavity that confines the electromagnetic field.

We solve this challenge by producing purified suspensions of gold nanoparticle dimers linked by a single DNA double strand exhibiting one a single dye molecule. Tuning the electromagnetic field enables unprecedented photophysical properties, such as decay rates and excitation cross-sections enhanced by more than one order of magnitude compared to an optimized, commercial chromophore.

Free access alternative pdf version of the letter can be found via arXiv:1210.6790

Optical fiber probes are generating a large interest for portable Raman spectrometers. However, the use of conventional fibers is severely limited by the high luminescence background generated in the silica, which complicates the signal processing and/or the probe implementation.
We solve this issue in a recent article published in Optics Letters by using a new type of hollow core photonic crystal fiber probe for Raman spectroscopy and endoscopy. Thanks to a design based on a large pitch Kagome lattice, the transmission range spans over 150nm, enabling both the excitation and Raman beams to be counter-propagating through the same fiber.
Compared to earlier work, our approach combines several novel key features: (i) the very simple optical configuration, (ii) the two orders of magnitude reduction in silica background noise, and (iii) the large spectral bandwidth for Raman shifts.

Check our work recently published online at the Advanded Materials website. For the first time, we investigate experimentally the luminescence enhancement of a single quantum dot deterministically coupled to a plasmonic gap antenna. We also provide the full information hidden behind this luminescence enhancement by quantifying independently the excitation enhancement and quenching effects.

Our approach combines two technological breakthroughs: (i) the custom-synthesis of colloidal QD with controlled multiply excited states, and (ii) the deterministic QD-antenna coupling via double step e-beam lithography. A remarkable feature is that excitation enhancement can still be investigated even in the presence of strong quenching losses affecting the emission. This study provides new routes to experimentally investigate the physics of optical antennas, and optimize the excitation and emission processes independently for the future development of bright single-photon sources and biochemical sensors.

This research is done in close collaboration with the groups of Dan Oron at Weizmann Institute of Science and Romain Quidant at ICFO, and is conducted in the scope of the NaBi associated European laboratory.