Controlled-release microcapsules

Gel-based capsules that can be individually opened with a precisely aimed blast from a laser could be a new way to control reactions or deliver drugs.

Japanese chemists have developed a light-responsive gel that will switch to a liquid-like sol state when triggered by UV light. Droplets of the gel can be used as controlled-release capsules for reactive cargo, say Itaru Hamachi and colleagues at Kyoto University. And a finely focussed laser can be used to fuse two gel capsules together, allowing their contents to mix together and react.

Hamachi's hydrogel consists of a self-assembled, supramolecular network of small organic molecules which each incorporate a carbon-carbon double bond. UV light triggers this alkene group to isomerise, converting a linear molecule into a bent one.  This disrupts the supramolecular structure and turns the gel into a sol.

Hamachi used this effect to selectively join two adjacent gel capsules, one carrying an enzyme and the other a fluorogenic substrate. Using a carefully focussed laser beam to partially fuse the two gel capsules, a readily detectable fluorescent dye was produced as the enzyme and substrate mixed.

'This is a very interesting, elegant concept,' said Jan van Esch, who researches hydrogels at Delft University of Technology in the Netherlands. 'This approach could bridge the gap between reactions done in test tubes and by microfluidics, both in terms of scale and the surface effects you get with small volumes. And a nice thing about the technique is it can be readily adopted by other researchers, you don't need any special equipment to apply it,' he said.

According to the Kyoto team, the potential applications of the process range from microfluidics to drug delivery. 'In the future of nanotechnologies, biomolecules such as DNA, RNA, proteins and cells are undoubtedly key players,' said Hamachi. 'Thus, the development of materials which can encapsulate, isolate and manipulate biomolecules at the single molecule level will become increasingly important,' he said.

James Mitchell Crow