Crystals go under cover

Fooling the human body by camouflaging inorganic particles as proteins.

The human body is usually fairly good at spotting inorganic particles, but US researchers have made its job more difficult by developing a peptide-based coating that can disguise the particles as proteins. So far, the researchers have only applied the coating to luminescent semiconductor nanocrystals but it could also be used to disguise inorganic devices.

Researchers at the University of California, Los Angeles (UCLA), and the University of California, Berkeley, got the idea for the peptide coating from nature. Certain plants and bacteria produce cysteine-rich peptides called phytochelatins, with which they soak up toxic metal ions. These proteins can form complexes with metal ions that are very similar to synthetic CdSe semiconductor nanocrystals.The potential of these nanocrystals in biological imaging has been restricted by their highly hydrophobic nature. The researchers made the nanocrystals less hydrophobic using synthetic versions of hydrophilic phytochelatin peptides.

After investigating a number of different peptide chains, the team focused on a peptide with a hydrophobic adhesive domain comprising cysteine and 3-cyclohexylalanine residues, which could bind to the CdSe/ZnS nanocrystals. This binding was highly stable and did not greatly affect the luminescence of the nanocrystals.

’We can use these coated particles to track the proteins in a live cell and conduct a range of studies at the molecular level,’ explains lead researcher Shimon Weiss, professor of chemistry at UCLA.

Ultimately, Weiss envisages using the peptide coatings to provide electrical contact between nanoscale inorganic electronic devices and functional proteins, to develop a range of novel drugs and catalysts.

Jon Evans