Diatoms are unrivalled architects at the nanoscale. The silicon shells of these single-cell algae are porous, highly symmetrical 'boxes' with species-specific, lace-like patterns in nanometre dimensions. Similar control of nano-structuring processes would be useful in many areas of nanotechnology, but mimicking the diatom's construction work has proven a major challenge (Chem. Brit., July 2003, p33).

Now, researchers in the US have found that the natural diatom shell can be used as a foundation for artificial nano constructs, a much more accessible route than biomimetics.

Chad Mirkin and colleagues at the Northwestern University in Evanston, Illinois, US, stripped diatoms down to the pure inorganic skeleton by immersing them in an acid bath aptly named the 'piranha'. This treatment left the shells susceptible to functionalisation with an amino-silane reagent. The free amino functions were in turn used to couple DNA oligonucleotides to the diatom shells. Using complementary DNA strands coupled with gold particles (13nm) in order to make the coating easily visible in the electron microscope, the researchers demonstrated that the entire surface of the empty shell can be functionalised and covered in artificial materials. Moreover, the researchers could add up to six further gold layers onto the first one.

The procedure worked equally well with two different diatom species, Synedra and Navicula. Thus, researchers might one day choose any of the thousands of different diatom species for their specific purposes. For example, to create a particular nanoscale pattern in gold (or any other) particles, one would only have to find a matching diatom shell and build on that. Alternatively, one could 'easily modify the diatom surfaces with many different functional groups', suggests Mirkin. For example, one might produce microscopically small DNA arrays in large copy numbers.

Michael Gross