"We decided to study the shortest molecular element that we suspected may be able to mediate the molecular recognition and self-assembly processes - the core-aromatic moiety of the Alzheimer's beta-amyloid," researcher Ehud Gazit told nanotechweb.org. "From a medical point of view, we were able to demonstrate that a peptide as short as a dipeptide - which is the shortest that one can get - contains all of the molecular information needed to mediate events of molecular recognition and self-assembly."

The scientists worked on the Alzheimer's β-amyloid diphenylalanine structural motif, and while trying to make the NH2-Phe-Phe-COOH dipeptide soluble at very high concentrations in an organic solvent, they discovered that the material rapidly self-assembled into nanotubes. Adding the nanotubes to boiling ionic silver solution and then reducing the silver with citric acid created silver nanowires inside the tubes. Finally, to remove the peptide mould, the researchers added proteinase K enzyme. This left individual silver nanowires roughly 20 nm in diameter.

"The casting of metal nanowires within a degradable bioorganic mould is an example of the strength of the interdisciplinary combination of biological systems - which have properties such as molecular recognition and biodegradability - with the ability to fabricate solid-state inorganic nanostructures," said Gazit. "This is the first time that the casting of discrete and uniform metal nanowires of higher persistence length has been reported. Such nanowires should have ample applications in molecular electronics and other nanotechnological uses."

For applications such as nanotube-based biosensors and hollow tubing of nanofluidic circuits, the researchers say it would be desirable to have enzymatically stable nanotubes. For these cases, they cast nanowires in nanotubes formed from the D-amino acid analogue of the peptide, NH2-D-Phe-D-Phe-COOH. These nanotubes were not affected by treatment with proteinase K.

Now, Gazit and colleagues plan to use peptide nanotubes to cast other conducting, semiconducting and magnetic materials into nanorods and nanowires, and to integrate the tubes into nanoelectronic, nanophotonic and microelectromechanical systems assemblies. "One of the immediate directions will be to evaluate the potential use of the tubes as field emitters," added Gazit.

The researchers reported their work in Science.