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nanotimes News in Brief

10-10/11 :: October/November 2010

Material // The Most Rigid Organic Nanostructures

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hud Gazit, Itay Rousso, and a team from the Tel Aviv University, the Weizmann Institute of Sci-

ence and the Ben-Gurion University of the Negev (Israel) have now introduced organic nanospheres that are as rigid as metal. Nanoscale biological structures often exhibit unique mechanical proper- ties; for example spider silk is 25 times as strong as steel by weight.

The most rigid synthetic organic materials known to date are aramids, such as Kevlar. Their secret is a special spatial arrangement of their aromatic ring systems and the network of interactions between their planar amide bonds. The new nanospheres are based on a similar construction principle. However, unlike the large polymeric chains, they are formed in a self-organization process from very simple mole- cules based on aromatic dipeptides of the amino acid phenylalanine.

Nanoscale biological structures often exhibit unique mechanical properties; for example spider silk is 25 times as strong as steel by weight. The most rigid synthetic organic materials known to date are ara- mids, such as Kevlar. Their secret is a special spatial arrangement of their aromatic ring systems and the network of interactions between their planar amide bonds. The new nanospheres are based on a similar construction principle. However, unlike the large po-

lymeric chains, they are formed in a self-organization process from very simple molecules based on aro- matic dipeptides of the amino acid phenylalanine.

Using an atomic force microscope, the scientists examined the mechanical properties of their na- nospheres. This device uses a nanotip (cantilever), a tiny flexible lever arm with a very fine tip at the end. When this tip is pressed against a sample, the deflection of the lever indicates whether the tip of the needle can press into the sample object and how far in it can go. A metal needle was not able to make any impression on the nanospheres; only a needle made of diamond was able to do it.

The researchers used these measurements to calcu- late the elasticity modulus (Young’s modulus) for the nanospheres. This value is a measure of the stiffness of a material. The larger the value, the more re- sistance a material has to its deformation. By using a high-resolution scanning electron microscope equipped with a nanomanipulator, it was possible to directly observe the deformation of the spheres.

For the nanospheres, the team measured a remar- kably high elasticity modulus (275 GPa), which is higher than many metals and similar to the values found for steel. This makes these nanostructures the stiffest organic molecules to date; they may even