Science 335, 690–694 (2012)

Credit: © 2012 AAAS

Hollow microcapsules have proved useful for a number of applications because of their ability to encapsulate molecules — or even larger ensembles such as cells — and shelter them from bulk environments. There are a range of different processes that can be used to make synthetic microcapsules, including layer-by-layer deposition onto colloidal templates as well as self-assembly approaches. Each of these techniques has its own drawbacks, and an ideal method would produce relatively monodisperse capsules into which cargo can be loaded efficiently.

Now, a team of researchers at the University of Cambridge led by Oren Scherman and Chris Abell have shown how microfluidic droplets can be used to prepare porous supramolecular microcapsules with a high degree of monodispersity. Their approach takes advantage of the host–guest properties of cucurbit[8]uril (CB[8]) — a toroidal molecule that can accommodate two different aromatic groups inside its central cavity. Aqueous solutions of CB[8], gold nanoparticles functionalized with electron-deficient aromatic ligands, and a water-soluble polymer with electron-rich naphthol side chains were prepared. These were then flowed into one arm of a T-junction in a microfluidic device. Oil flowing perpendicularly to the aqueous stream sheared off microdroplets containing the three building blocks, which then assembled into hollow microcapsules as the polymer chains and nanoparticles are stitched together by the CB[8] hosts.

Both the nanoparticle and polymer components can be tuned to give different properties from the resulting microcapsules. Incorporating a dye into the polymer backbone enabled the shell to be visualized with a confocal microscope (pictured, left) in the same way that a dye-labelled guest trapped inside the capsule was imaged (pictured, right).