Cooking up nanowires

The researchers put the hollow nanotubes in a solution with silver ions, producing silver-stuffed nanotubes. Then by dissolving the peptide tube with an enzyme, they were left with silver nanowires. The New York Times described it like this: ‘Imagine a …

The researchers put the hollow nanotubes in a solution with silver ions, producing silver-stuffed nanotubes. Then by dissolving the peptide tube with an enzyme, they were left with silver nanowires. The New York Times described it like this: ‘Imagine a tantalizing plate of manicotti – tubes of pasta stuffed with a seasoned ricotta-egg mixture. In a laboratory at Tel Aviv University in Israel, researchers have been cooking up a kind of manicotti of their own. Instead of pasta tubes, however, they use a peptide molecule – a short chain of amino acids – that assembles itself into tiny tubes. And instead of ricotta cheese, they stuff their tubes with silver. What results are nanoscale wires, on the order of 20 billionths of a meter in diameter.’

That analogy may help you visualize what a nanoscale wire looks like and how it’s made, but what exactly is it good for?

According to researcher Prof. Ehud Gazit, the cast silver nanowires could conduct electricity for stable biosensors and circuits. The TAU research is the first time that discrete and uniform nanowires have ever been synthesized, and the achievement has aroused great interest among academic researchers, and in relevant industries around the world.

Combining biology and inorganic chemistry, Gazit and research assistant Meital Reches studied the beta-amyloid protein fibrils that accumulate in the brains of Alzheimer’s patients. These proteins also accumulate in other parts of the body, causing type II diabetes and prion diseases.

The TAU team mapped a tiny segment of the protein that mediates the process in which the brain plaques are created. When they looked at it under an electron microscope, they found to their surprise that this element creates hollow tubes that look like macaroni but are about 100 billionths of a meter in diameter and a few microns long. These are visible only through an electron microscope.

“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,” 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 researchers, who describe their work in the current issue of Science, had a novel approach when they realized the tubes were hollow. By putting them in a solution with silver ions, and then reducing the ions to elemental silver, they produced silver-stuffed nanotubes – nanomanicotti, as the Times called it. Then by dissolving the peptide tube with an enzyme, they were left with silver nanowires.

“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.”

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.

Their work, regarded as a major achievement not only in nanotechnology but also in biology, has received accolades from around the scientific community. According to Dr. Susan Lindquist, Head of Whitehead Institute, Cambridge MA, USA, “this study of the remarkable properties of peptides, initially investigated because they might yield insights into Alzheimer’s disease, provides a vivid example of how biological research can take the most unexpected turns, with potential benefits never dreamed of at the start.”

Dr. Shuguang Zhang, Associate Director, Ceneter for Biomedical Engineering, Massacusetts Institute of Technology (MIT), Cambridge MA, USA reinforced that view, adding, “Gazit [and his team] have achieved something others have tried for many years, from a complete different route. This again demonstrates the crucial aspect of the curiosity-driven research that can eventually alter a concept or start up new industry. Funding for basic science has been eroded due to short-sightedness of many governmental funding agencies and economic down turn. This discovery should remind all of us the power of basic and curiosity driven research, the well springs of breakthrough advances in both science and technology.”