Light triggers nano-container to release cargo and dismantle itself

A novel nano-container can take up hydrophobic compounds of various sizes and shapes in water and then release them in response to light

Original source: Materials Today

Researchers at the Tokyo Institute of Technology (Tokyo Tech) in Japan have developed a nanosized container bearing photoswitches that can take up hydrophobic compounds of various sizes and shapes in water and then release them in response to light. The photoswitches also allow the containers to be reused after the successful release of their cargo. This novel system represents a versatile platform for future developments in fields such as materials chemistry and biomedicine.

Researchers at Tokyo Tech’s Laboratory for Chemistry and Life Science developed a micelle-type nano-container that can be switched between its assembled and disassembled state via illumination with light. The light stimulus triggers a structural change in the nano-container’s amphiphilic subunits, closing their integrated binding pocket and instigating their disassembly.

In a paper in Nature Communications, Lorenzo Catti, Natsuki Kishida, Michito Yoshizawa and their co-workers describe their success in combining the use of water and light in an environmentally benign delivery system. “Water and light are abundant and clean resources on earth,” explains Yoshizawa. “Active use of both of them in synthetic and materials chemistry has seldom been accomplished so far, but is an urgent necessity for the development of sustainable modern technologies.”

The researchers’ achievement is based on a small design change in the subunit of the nanosized container. By moving the two polyaromatic panels on an earlier amphiphilic compound closer together by one carbon atom, the researchers enabled a photochemical reaction between the panels that results in the closing of the binding pocket. In addition, the group also showed that this reaction is partially or fully reversible by exposing the container to light or heat, respectively.

This study is part of the group’s ongoing effort towards environmentally benign nanoflask systems with controllable functionality. The new system can be considered an ‘aromatic micelle’, a concept that was first introduced by the group in 2013.

Uptake of water-insoluble guest molecules into the container was shown to be easily achievable via a simple grinding protocol. Adding water to the resulting solids produced characteristically colored solutions, which displayed UV-visible absorption bands attributable to the bound guest molecules.

The flexibility of the nano-container allowed the uptake of a wide variety of compounds, such as rod-shaped and planar dyes and spherical fullerenes, in water. Quantitative release of the guest compounds could be achieved by illuminating the aqueous solution for 10 min at room temperature. The released, water-insoluble guests could then be successfully recovered via simple filtration, giving rise to a clear colorless solution containing only the dismantled amphiphiles.

“In a biomedical context, the developed system holds great promise for future progress in non-invasive delivery of biomolecules and synthetic drugs,” Yoshizawa says. Future improvements to the system will include allowing the use of a weaker light source for illumination, which will bring the system one step closer to the envisioned in-vivo delivery application.