Heavy metals coming from industrial waste, such as mercury, lead, cadmium, nickel, and zinc are some of the most dreaded pollutants in water, and EU laws strictly limit their concentration in the water we drink. Measuring these pollutants is commonplace but cumbersome. A sample of water has to be collected and carried to a laboratory, where it takes days (at best) to get the results.
A group of researchers at the Ecole Polytechnique (EP) in Palaiseau, near Paris, have developed a tiny film that could speed up the process dramatically. The "nano-factor" is within the film itself: billions of nanopores per square cm that trap metals like a sponge, making them immediately available for analysis. Their new system is portable, provides immediate results, and therefore may change the way we monitor water quality.
François Plais, Technology Transfer Officer at the Ecole Polytechnique, is an engineer with industry experience who is supporting the team that developed the sensor. The team include Marie-Claude Clochard, Travis Wade and Haad Bessbousse
How does your system work?
Research teams and companies around the world are developing membranes to filter water. Our researchers realized that we could adapt the structure of the membrane to work as a trap for metal ions. The two ideas are similar and opposite: a filtering membrane is a tiny sheet of polycarbonate with holes of a diameter of 30-40 nanometers, called nanopores, that let the water flow and filter out impurities. Our sensor membrane, instead, is made with another polymer called PVDF, and with nanopores that trap water and any metal ions that come with it. Basically, it works like a sponge. The system also works as a sensor, because metals ions change the electrical properties of the membrane. If we apply two electrodes at the membrane, we can measure the concentration of metals with a standard electrochemical test, which is relatively straightforward.
What are the advantages compared to the existing technologies?
With our system you don't need to bring a sample to the laboratory, because you can use it on site. At the same time, our data show that the sensitivity and accuracy are comparable to the current laboratory standards.
Can you mention some possible applications ?
Our system may be ideal to assess the quality of drinking water pumped from lakes, reservoirs or rivers, for example, or to monitor pollution from industrial waste. By providing immediate results, it could really change the way we monitor water quality, as far as heavy metals are concerned.
What are you going to do next?
We still need to validate our laboratory results in a real-world setting. We have now found a partner that will allow us to do that, and we are now working on this new phase of the project.