Spheres of influence

Technology which allows researchers to remotely control chemical reactions on a micro scale has been developed at Saudi Arabia's King Abdullah University of Science and Technology.

Lead researcher Peng Wang and his team used 'liquid marbles', tiny spheres of complex particles which hold a droplet of water ready to initiate a chemical reaction, that can move through a liquid medium without leaking until exposed to low pH.

The encapsulating sphere, or 'marble', is made of shell-structured, stimuli-responsive magnetic particles with a magnetite core. This allows it to be remotely controlled by a magnet. The core of the particle is covered with a silica shell with pores ranging from 2 to 50 nanometres wide, which can be further used to incorporate functional molecules. It is grafted with a pH-responsive polymer that causes it to be hydrophobic when in higher pH levels, sealing the liquid inside. Once pH drops below 2, the sphere breaks down, releasing the liquid inside.

The KAUST researchers found a way to remotely rupture these liquid marbles by exposing them to UV light. The team loaded the mesoporous silica shells of the particles that make up the spheres with a photoacid generator, a commercially available molecule that, when exposed to UV light, releases an acid. The locally generated acid causes the shells of the liquid marbles to become hydrophilic and collapse, releasing its content and initiating chemical reactions on demand.

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