recent research work

Following up with the story of the smallest single molecule detection apparatus ever, and first portable FCS system with true single molecule routine sensitivity, my team has recently published a technical note in the Spectra Analyse magazine. This is also an introduction as to why fluorescence correlation spectroscopy is a powerful method to extend standard fluorescence spetroscopies. A free reprint can be found here.

Summary: Fluorescence correlation spectroscopy (FCS) is a versatile method that would greatly benefit to remote optical fiber fluorescence sensors. However, the current state-of-the-art struggles with low detection sensitivities that prevent the extension of fiber-based FCS down to the single-molecule level. Here we describe a novel probe based on an optical fiber combined with a dielectric microsphere to perform FCS analysis down to the single fluorescent molecule level. This offers new opportunities for reducing the bulky microscope setup and extends FCS to remote or in vivo applications.

My team has released an article in the October 7^th issue of the Journal of Physical Chemistry C.

A wide range of studies had been recently devoted to nanoaperture arrays as substrates to enhance the Raman scattering spectrocopy of adsorbed molecules. However, only partial information is known concerning the case of a single nanoaperture. Our paper fills this gap, and discusses the first quantitative evaluation of the SERS enhancement factors on single nanoapertures milled in optically thick gold films.

This work has three major aspects of interest to the SERS community: 

1) Nanoapertures milled in noble metal films form interesting SERS substrates thanks to their rational and tunable design, controlled surface enhancement, and intrinsic robustness. We discuss the different design parameters yielding to optimum SERS enhancement already in a single aperture which can be used to further improve the SERS substrates with nanoaperture arrays.

2) We discuss different ways of expressing the SERS enhancement factor, and show excellent agreement between experimental results and numerical simulations.

3) Most experimental studies of controlled SERS substrates skip the issue of the adhesion layer between the gold nanostructure and the glass substrate. We experimentally demonstrate that the adhesion layer has a crucial effect on the SERS enhancement, and needs to be fully considered while designing nanosubstrates for high-sensitivity spectroscopy.

A reprint for personal use only is freely available here.

Meet me at the TOM3 Nanophotonics and Metamaterials during the next annual meeting of the European Optical Society.

I'll have a talk on Thursday October 28th 10am. While most of the presentation should focus on our recent methods to experimentally characterize optical nano-antennas, I'll also show some of our most recent (unpublished) results on controling fluorescence directional emission.

Check out in the August issue of ACS Nano, a paper in collaboration with the Weizmann Institute of Science on the use of colloidal quantum dots to probe the local field enhancement on photonic antennas.

Plasmonic nanoantennas constitute a very active area of nanosciences, and have turned into essential devices to manipulate light at the nanoscale. Various spectroscopic methods are commonly used to quantify the overall amplification brought by an optical antenna on the emitted signal. However, experimentally characterizing the antenna’s response at the excitation frequency solely remains a scientific and technical challenge. Such characterization is highly needed to fully understand and optimize the antenna’s design.

Our paper describes a novel experimental method to directly characterize the antenna amplification on the excitation field independently on the emission process. We take advantage of the complex transient photoluminescence dynamics of colloidal quantum dots to probe photonic nanoantennas made of dielectric microspheres and gold nanoapertures.

This work has four major aspects of general interest:  

1) we describe a novel and direct approach to quantify the electromagnetic amplification on an optical antenna for the excitation process only.

2) we demonstrate a new form of enhanced (nonlinear) light-matter interaction at the nanoscale via the increased doubly excited state formation on nanoantennas

3) we introduce a novel use of multiple excited states in colloidal quantum dots for nanophotonic applications. This effect is impossible to obtain with (organic) molecular systems.

4) we show excellent agreement between experimental results and numerical simulations.

My group has recently developed an integrated system for compact and portative single molecule fluorescence analysis without using any microscope or microscope objective.

The system is based on our patented technology based on a glass microsphere at the end of the optical fiber. The microsphere works as a tiny lens to focus light with focusing capabilities close to that of a high-quality microscope objective.

The system is capable of single molecule fluorescence correlation spectroscopy (FCS) and fluorescence lifetime histograming (TCSPC). The size is roughly that of an A3 format, that makes it the world’s smallest FCS system to date, and much more integration is readily feasible.

See a complete article here.