Viruses, vesicles or metal oxides, aqueous media contain corpuscles of a few dozen nanometres whose identification is now a major issue. Until now, however, heavy and expensive technologies, such as the electron microscope, had to be used to detect them. Researchers from ENS-PSL and ESPCI-PSL have devised an innovative optical technology that enables the rapid detection and characterization of these objects. Applications range from immunotherapy to pollution monitoring.
Claude Boccara - Until now, we have been working mainly on liquid media, but our technology also makes it possible to track these objects in gaseous media, in the air, for example.
Even if it is limited to liquids, it opens onto various environments, from the human body to the oceans. It was during an oceanographic mission that the first intuition of our technology was born. Martine Boccara, my sister, is a researcher at the Biology Institute (IBENS) of École Normale Supérieure (ENS-PSL). Her work focuses on aquatic virus populations. Viruses, as you probably know, are at the frontiers of life: they contain DNA but do not have all the characteristics of organic life - for example they cannot reproduce themselves and need a host cell. They are very small: from 30 to 100 nanometers, which is much less than a bacterium. They cannot be seen under an optical microscope, which has a 500 nanometres resolution. You need an electron microscope to observe them.
Viruses are mainly known as pathogens, sometimes terrifying – think of the Ebola virus, for example. But they are also the subject of renewed interest in what is called phage therapy, a method developed in the 1930s that uses bacteriophage viruses (also called "phages"). It has been marginalized by the discovery of antibiotics, but these are now victims of their success: more and more bacteria are resistant and phage therapy takes again all its interest.
A few years ago, while participating in the Tara Oceans interdisciplinary project for the study of plankton, Martine began to think seriously about the limits of the technologies available to detect and characterize viruses in the marine environment: chemical or microbiological analyses, electron microscopy, laser techniques. All these techniques have in common that they follow a specific category of nanoparticles. They are very practical when you already know what you are looking for, but they meet their limits when you try to characterize an entire field. Some, moreover, only support a laboratory environment - a simple, isolated environment, protected from noise and vibration, for example. Finally, they are often expensive.
What if other methods were possible? We discussed it, and very quickly the idea emerged of using high sensitivity optical methods, cameras with a resolution of one or two million pixels applied to a very small field: about 100 microns by 100 microns. What remained to determine was how to process the data collected: how to characterize the nano-objects present in the field of these cameras?
The heart of our technology is interferometry. It is a measurement method that exploits interference between two waves. Interferometers are widely used in the industry, where they have many applications. The method we have developed is optical interferometry. It articulates a data capture, in this case a film of a few seconds, and an analysis of these data, which processes and analyzes the level of light scattered by the nano-objects. Think of dust grains in a sunbeam: you don't see the grains themselves, but you see the light they scatter. It's the same principle. Our technology does not "see" the nano-objects themselves, but a light effect that allows us to detect their presence and characterize them (what movement, what size, etc.). We measure the amount of light scattered by objects (which is a function of size and refractive index) and the type of movement that drives them.
Think of dust grains in a sunbeam: you don't see the grains themselves, but the light they scatter.
For example, inorganic particles, say metal oxides, are animated by a random motion (called "Brownian") that allows them to be identified. They can be distinguished from each other because the characteristics of this movement depend mainly on their size.
Viruses, on the other hand, have a very different movement in only one direction. Here again, when filming a field in which one or two hundred particles are moving, they can be easily detected.
Yes, and you will see that this brings us to applications. Among the nanometric objects, you also have vesicles, which are groups of self-organized molecules, with an aqueous membrane and a core. The membrane is a two-layer surfactant. The vesicles are secreted by the cells and you can describe them as biological messengers.
To detect their presence, count them and characterize them allows to characterize an environment, for example the vital fluids which circulate in the human body or the interior of the intestines: these messengers are involved in certain pathologies, and their detection is an element of diagnosis. The same applies to viruses.
In the same spirit, the detection, characterization and counting of metal oxides can help qualify an environment, for example for measuring the pollution of a river or lake.
The rapid and reliable detection of these different nanometric objects is a big stake in various contexts. Sectors such as medicine (phagotherapy, immunotherapy, diagnostics), the environment and agriculture can benefit from this advance, especially since a large part of our technology can be automated. Another advantage is that an analysis requires only a small quantity of product, an economy of scale that in some contexts can make a difference.
The statutes were tabled at the end of September and we moved quite quickly to development. A prototype has been produced, and five demonstrators are being deployed within five "opinion leaders," public or private laboratories whose feedback we will collect; this will serve us both to identify the most interesting uses (and therefore the most promising markets), but also to constitute a reference for marketing.
We relied on the development services of the Langevin Institute, of which I am a member, the ESPCI and PSL, as well as Quattrocento, a company builder specializing in life sciences. They interface with the markets, and thus contribute to profiling technology and defining it not only as an original scientific object, but as a device oriented towards uses. The simplicity of our technology, its capacity to make measurements in complex environments, its robustness and its ability to operate in an environment that is not the ultra-protected environment of a laboratory, all this can define a product that can meet the needs of users in various sectors, such as those I have mentioned but also others, barely emerging, like synthetic biology. But commercial development, which will involve strategic choices, does not exhaust the potential of this technology, and the academic work continues.