Filotea Crasovan Neacsu

Keeping in line with the first article regarding nanoplasmonics, we have interviewed Romain Quidant, currently Professor of Nanophotonic Systems at the Department of Mechanical and Process Engineering from ETH. In 2002, Romain Quidant received a Ph.D. in Physics from the University of Dijon (France). Right after, he joined ICFO as a postdoctoral researcher. In 2006, he was appointed Junior Professor and group leader of the Plasmon NanoOptics group. Three years after, he became tenure Professor both at ICFO and ICREA. His core expertise is in fundamental nano-optics, mostly by combining physics with other disciplines of science, as well as in technology transfer. He has won 4 grants as well as several international and national prizes. Since 2019 he has started serving as the executive editor of ACSPhotonics (American Chemical Society).

First of all, how did you find your professional vocation (for Physics and nanoplasmonics): was it inspired or based on a personal life-changing experience? Continuing that point, when did it happen? 

I believe my trajectory has more than one inflection point. I should probably present first why I chose a scientific career and then how my passion followed the path of Physics, and brought me to the specialty of Photonics. 

I could say that the entry into science was first based on my interest for Mathematics and Physics. But science was also a way to express my creativity.  I always like to draw a parallel with  my brother, who is an artist. We often highlight the similarities of our respective professions, just the support differs. 

The rest of my path to research is something that came along University studies. As young students we usually miss the big picture, and the people you meet are key influences. I had a professor in Mathematics for Physics whose teaching methods were very different. He aimed at making us think out of the box and see science in a global way. He ended up being my Ph.D. supervisor. Working with him in the field of Photonics made me see how this field was fun and transversal with the potential to have a great impact on society. 

I am sure that daily, the monotony of life cannot strike us in an immediate way, unless we talk about massive changes, for instance, the Sars-CoV-2 pandemic: what do you do to keep your passion alive?

The beauty of research is that you constantly reinvent yourself. Research helps you keep the flame and passion for science alive: you identify a problem to solve, explore different routes, after many failures you identify a solution and share it with your peers in a publication and at conferences. Then you restart the process along new directions, tackling new problems, and growing your knowledge. Although I’ve been using a similar scientific toolbox over the years, I have used it in many different aspects of science and technology, and this interdisciplinarity has always kept me out of my comfort zone, in a constant learning phase. 

During the most critical days of the covid pandemic, without the possibility of working in the best conditions, it has become clearer to me how passionate I am about science.

Thirdly, I have become pretty interested in how nanoplasmonics can be part of our life, even taking part in medical procedures: could you give us more details regarding the discovery of these oscillations?

There is not a single specific experiment which gave birth to the field. Plasmonics, like many other scientific fields, were born from multiple independent contributions. 

The first known manifestation of nanoplasmonics brings us back to the Roman stained glass artwork whose vivid and persistent colors are now understood as the consequence of noble metal nanoparticles embedded in the glass matrix. Of course, at that time, scientists did not have the tools to understand the involved physics, and their knowhow was only based on trial and error.

One has to wait for the beginning of the XXth century and the development of the Mie theory (Gustav Mie – 1908) to understand how light interacts with nano and microparticles. The Mie theory allows us to rigorously calculate their light scattering and also predict the existence of particular optical resonances, including plasmon resonances.

Later on, during the 80s, physico-chemists got interested in surface-enhanced Raman scattering. Raman spectroscopy, discovered by Sir C. V. Raman in the 20s, captures the vibrational fingerprint of molecules. Researchers noticed that this very weak signal gets greatly enhanced for molecules in the close vicinity of noble metallic nanoparticles supporting plasmon resonances. Although the field was not named Plasmonics at that time, Surface-enhanced Raman spectroscopy was a true catalyst for further research on the optical properties of metallic nanoparticles. The name Plasmonics was eventually coined in 2004, by researchers at Caltech, when the field already brought together many groups across different scientific communities, from Physics, Biology to Chemistry.

My first experiment with nanoplasmonics brings us back to my Ph.D. thesis initiated at the end of the 90s. I was working on ways to concentrate and guide light through subwavelength sections. In particular, I studied how electromagnetic coupling within periodic arrangements of gold nanoparticles could funnel light over specific bands of the visible spectrum.

I remember that you once told me that perhaps certain results of the research wouldn’t be conclusive for the set objective of the study, but it could be recycled for another scientific use. Has it happened when working with nanoplasmonics?

Indeed, research often requires adaptation and being inventive when facing obstacles.

Plasmonic nanoparticles are like nano lenses. They can collect light from a given wavelength range and concentrate it at their surface. The ability to concentrate photons in such a tiny volume is a true advantage, but the fact that there are losses via Joule heating was perceived by the community as a major drawback. Since heating is intrinsic to plasmonics and cannot be circumvented, we chose in my group to turn it into an asset that could benefit different applications requiring ultra-precise heat control.

In this context, my team has been working for years on how nanoplasmonics could contribute to cancer therapy. The main idea is to inject biofunctionalized nanoparticles in the bloodstream of mice to get them to specifically attach to cancer cells. Using laser illumination, decorated cancer cells would die upon light-induced heating of the nanoparticles. However, the problem when delivering nanoparticles intravenously is that they tend to accumulate in the liver, which may cause cytotoxicity. 

Recently, in close collaboration with Hospital Clinic and IDIBAPS, we turned this problem into an asset, by treating a liver pathology: fibrosis, a disease in which the liver (especially, stellate cells) loses its ability to regenerate. If not treated, it can evolve into cirrhosis and even cancer. The results of this new study were quite promising, showing a clear decrease of fibrotic tissues in treated mice. 

Nanoplasmonics has been used in the context of quantum optics, in particular to control the emission of quantum emitters, like quantum dots. By modifying the environment of the emitter, one can modulate the way it emits, for instance making it brighter. In a similar way as placing our quantum emitter between two mirrors would modify its emission, a quantum dot properly coupled to a plasmonic nanoparticle could emit much more photons that it would do otherwise. Researchers believe that this could be highly relevant to design more performant single photon sources.

Which would be the message that you would like, both as professor and Physics researcher, to give out to the students that read our magazine?

The main message that I would like to convey to all students is not to give too much importance to the artificial barriers created between fields of science. Important questions are most of the time interdisciplinary and require problem solvers to have a global vision over science and technology. For instance, if we take a look at a pragmatic example from our everyday life: our smartphone.  It is a good illustration of a tremendously sophisticated technology that builds upon the latest advances of electronics, photonics, cameras, GPS, sensors, etc…

Image source

Romain Quidant: Department of Mechanical and Process Engineering, EHT. The great potential of small dimensions Available from: [Available since 22nd May 2020]

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