I am currently developing two research themes. The first, applied theme concerns ultra-sensitive molecular detection in complex environments. The second, fundamental theme explores the use of nanoparticle-based semiconductors as substrates for the SERS (Surface Enhanced Raman Scattering) effect. These themes stem from the intersection of my professional background and my desire to contribute to water management in the context of climate change.
Ultra-sensitive Molecular Detection
The SERS effect relies on the excitation of electromagnetic and chemical phenomena by light, such as surface localized plasmons (LSP), hot spots, or tip effects that amplify the electric field and enhance Raman scattering by several orders of magnitude. It is primarily this effect that is exploited in SERS-based sensors. Detection in complex environments presents specific challenges that can be likened to finding a needle in a haystack: do we know the shape of the needle? Is the haystack very large? Is the needle fragile?
I began exploring this theme by seeking to detect biomarkers in human fluids. The challenge here is working with molecules (proteins) that do not have a very intense Raman signal and are extremely fragile. I then became interested in detection in water. In this environment, the challenge is to find molecules present in a vast quantity of water. Surrounded by students, I worked on polycyclic aromatic hydrocarbons, emerging pollutants (paracetamol and estradiol), and I am now interested in pesticides and arsenic.
Plasmonics on Semiconductors
To specifically detect molecules, it is necessary to functionalize the surface of plasmonic nanoparticles with probe molecules. Most often, grafting is done using thiol groups that form strong bonds with the gold of the nanoparticles. We have also used diazonium salts. In this case, we have shown that this grafting could be made regioselective through the activation and polarization of plasmons. Previously, we had shown that a click chemistry reaction, which usually requires thermal or light energy input, could be activated by the presence of plasmons.
These results convinced me that plasmons could play a role other than enhancing Raman scattering through the SERS effect. Electron transfer is involved in the two reactions mentioned above. Having conducted my thesis work on a nanoelectronic component, I naturally wondered what role a semiconductor decorated with plasmonic particles could play in the SERS effect. This is how I became interested in the PIERS (Photo-Induced Enhanced Raman Spectroscopy) effect, in which the illumination of a semiconductor with UV light before SERS detection allows for even stronger enhancement. A cathodoluminescence study revealed the role of the Schottky barrier and the diversity of electron transfer processes that contribute to the enhancement of Raman scattering.
My Lab
For this research work, I can rely on the instrumental platforms of my laboratory, the LSPM (SEM, Raman spectrometer at various wavelengths…). I also have a Raman and UV-visible spectroscopy platform, as well as a chemistry lab.
The latest addition to this instrumental setup is a free-jet aggregate source. This instrument, developed by Richard E. Palmer’s team at Swansea University, allows the formation of a jet of molecular aggregates with a controlled number of atoms.
