Klajn points out that these molecules have a long history at the Weizmann Institute: “Two Institute scientists, Ernst Fischer and Yehuda Hirshberg, were the first to demonstrate the light-responsive behavior of spiropyrans in 1952. Later on, in the 1980s, Prof. Valeri Krongauz used these molecules to develop a variety of materials including photosensitive coatings for lenses. Now, 63 years after the first demonstration of its light-responsive properties, we are using the same simple molecule for another use, entirely,” he says.
The advantages of the medium-based approach are clear. For one, the particles do not seem to degrade over time – a problem that plagues the coated nanoparticles. “We ran one hundred cycles of writing and rewriting with the nanoparticles in a gel-like medium – what we call reversible information storage – and there was no deterioration in the system. So you could use the same system over and over again,” says Klajn. “And, although we used gold nanoparticles for our experiments, theoretically one could even use sand, as long as it was sensitive to changes in acidity.”
In addition to durable “rewritable paper,” Klajn suggests that future applications of this method might include removing pollutants from water – certain nanoparticles can aggregate around contaminants and release them later on demand – as well as the controlled delivery of tiny amounts of substances, for example, drugs, that could be released with light.
Dr. Rafal Klajn’s research is supported by the Abramson Family Center for Young Scientists; the Rothschild Caesarea Foundation; the Mel and Joyce Eisenberg-Keefer Fund for New Scientists; the estate of Olga Klein Astrachan; and the European Research Council.