Many biochemical processes in nature rely on a system being pushed out of equilibrium and then returning to its resting state automatically. An example is the light receptors in our eyes. On the molecular basis of light perception, a light-responsive molecule within these receptors isomerizes upon irradiation with light. At the same time, an enzymatic reaction converts the light-responsive molecule back to its initial state. If this would not be the case, the light receptor cells would not revert back to their dark resting state and would not be able to sense light repeatedly. Instead, an image would be engraved into our eyes like into a photographic film.

In an effort to create light-responsive catalytic nanosystems, we have prepared nanoreactors that react to light in a similar way. When irradiated with visible light, they are switched on. However, they only stay in their on-state as long as light is present. In the dark, they automatically revert back to their resting state in which their catalytic activity is switched off. The light-responsive nanoreactors were prepared by coupling a new kind of light-responsive molecules, Donor-acceptor Stenhouse adducts (DASAs), to block copolymers and allowing the polymers to self-assemble into polymersomes, i.e. hollow polymer nanocontainers. By conducting the self-assembly in the presence of enzymes, they are encapsulated in the polymersomes. DASAs were synthesized that absorb light of various color, so that nanoreactors could be switched by irradiation with either white, red or with green light. By using more than one enzyme, these nanoreactors allowed to control and orchestrate enzymatic cascade reactions by the different colored light in the same water solution. Indeed, it could be envisioned that by computing a sequence of light colors, different chemical products could be obtained in a predictable manner.

Such biocatalytic, light-responsive polymersomes could be used to produce drugs on demand, e.g. within a cell, or to release active compounds such as drugs in a fine-tuned, light-guided way. Moreover, our collaboration partners in this project, the group of Dr. Luciano Boesel at Empa, St. Gallen, aim to implement these nanoreactors in light-switchable plasters for drug delivery through the skin, which would enable a non-invasive delivery method of essential drugs to prematurely born neonates.