Quidant, who was recently awarded the Fresnel Prize 2009 that recognizes the highest level of excellence amongst emerging researchers in the field of photonics, is an ICREA researcher at the UPC's Institute of Photonic Sciences (ICFO) and a fellow of the Cellex Foundation Barcelona.

Quidant is among the leading researchers of a strategy called "plasmonic oncology" that will revolutionize cancer treatment. He is working on this groundbreaking research program thanks to the support of the Cellex Foundation Barcelona. The idea is to introduce gold nanoparticles into tumor cells, to which laser light would subsequently be applied. Thanks to the phenomena discovered by this French researcher, the nanoparticles would heat up to such a degree that the damaged cells would be completely burnt.

Nanoparticles are metal structures that measure just one millionth of a meter: they have a diameter ten thousand times smaller than that of a hair. What is revolutionary about this novel use of nanoparticles is that they can be designed in such a way that they can be selectively introduced into a patient's body so that they only penetrate damaged cells. Thus, the treatment would only affect tumor tissues without damaging healthy ones, as happens with chemotherapy and radiotherapy.

The system is based on the twofold outcome of the nanoparticle engineering carried out by the researchers. Firstly, the nanoparticles must be able to recognize damaged cells and, secondly, they must become excellent nanosources of heat. The former is achieved by coating the nanoparticles with molecules that detect and go into the cancer cells. In the latter case, minute metal structures are designed so that their shape optimizes the generation of heat in response to an external light source.

The project is still at the experimental stage and is being undertaken in collaboration with experts in medicine and biology. One of the key processes in the experimental work is the selection of the particles from the damaged cells, which are inserted once their possible toxicity has been minimized. In principle, gold is biocompatible and is readily evacuated by body fluids, but the researchers must make sure that the chemistry involved in the process does not affect the cells.

A nanolaboratory in a drop of blood

The interaction between light and gold nanostructures is not only useful for the treatment of cancer but also for its diagnosis. Romain Quidant is working on a chip that is made up of a multitude of metal nanostructures that are able to send a light signal when they come into contact with cancer markers. This "nanolaboratory" performs a vast number of analyses in parallel from a single drop of blood. Each metal nanostructure is coated in molecules (receptors) that are able to recognize and trap a specific cancer marker. When this happens, the nanostructure responds to the external light differently to when no markers are trapped.

The team led by Romain Quidant in this research line has already developed a nanosensor prototype designed to detect doping substances in the blood, such as the steroids that some sportspeople use.

The main advantages of this type of device are its small size (which makes it easy to use in developing countries where there are no laboratories, for example), and its great sensitivity, which would make it possible to detect cancer in its early stages of development when there is a low density of markers.

Quidant anticipates that the detector will be ready within the next ten years and that its applications will range from agro-food controls to the detection of hazardous industrial substances.

Plasmonics: from Gothic stained glass to the laboratory

The discipline of plasmonics underlies most of Romain Quidant's discoveries. This is actually the "secret ingredient" that, for example, gives stained glass windows in cathedrals such a distinct color. In fact, stained glass contains fine metal powder. The interaction of light with the metal electrons in a metal nanoparticle generates sound waves-plasmons-that display surprising behavior, such as the ability to emit light and heat in a controlled way.

This basic phenomenon of physics is the optical response of metal nanoparticles when they are sent a certain amount of light. For each well-defined type of light, a nanoparticle has an "optical resonance" that, on the one hand, generates a very intense, concentrated field of light on its surface and, on the other hand, heats up the particle. A plasmon is this resonance effect that characterizes the interaction of light with these nanoparticles, which results in the intense, localized field and the heat.

Photonics

From the mirrors used by Archimedes to burn enemy ships to the lasers used for current diagnoses and treatments, the history of light in technology has been the adventure of transforming an intangible, short-lived phenomenon into a powerful and versatile tool. Light has become an indispensable tool whose many benefits include its use to shape industrial parts; analyze chemical substances; perform operations to correct short-sightedness, moles and the loss of skin color; and as a source of clean energy. Its everyday applications include broadband Internet connections, CD players, barcode readers, printers and even the laser lights used at concerts.

Light is a leading-edge tool. Future applications include quantum computers and super-secure encryption, in addition to new nanometric technologies and minimally invasive systems that interact with live matter.