Build 'em small

The shells of microscopic ocean creatures could be the inspiration for a new approach to building components for a wide range of technologies from the lab-on-a-chip to miniature medical devices.

Conventional manufacturing techniques are too clumsy to build the microscopic components for future micromachines, believes Dirk Volkmer (http://wwwhomes.uni-bielefeld.de/dvolkmer/Volkmer_Group/). Now, he and his team at the University of Bielefeld, Germany, inspired by the microscopic marine organism, radiolaria, are building shell-like structures that might one day form the building blocks of such devices.

Exactly how biomineralizing organisms such as the ocean-dwelling radiolaria make their silica casings is little understood, but Volkmer and his colleagues have enough clues to help them emulate the building process and have synthesised some spiky silica structures that resemble radiolaria casings.

To make their mock shells, the researchers used a surfactant cocktail to form minute oil droplets in a water-based solution. The oil droplets contain a molecular metal oxide precursor, which polymerises on contact with water forming a polymeric metal oxide coating at the oil-water interface. Video microscopy revealed that star-shaped mineralized shells form on the originally smooth droplets' surface. The model reaction is disarmingly simple and, says Volkmer, is the first truly biomimetic approach! He compares it with lithographic techniques used to build up microscopic structures on a silicon chip but points out that his technique does not require sophisticated equipment to produce complex structures, just a reaction flask.

One of the first applications of these structures might be to use them as catalytic supports because they have a very high surface-to-volume ratio. Volkmer revealed to us that they are already investigating more sophisticated precursor compounds in their synthetic strategy, such as polymers and charged particles. These, he explains, could be used to create even more complex three-dimensional shells for other applications. It seems when it comes to nature: she sells seashells that chemists shoot for.

You can watch the growth of Volkmer's spiny shells if you have a DivX capable AVI movie viewer (The DivX codec is available from http://www.divx.com/divx/).