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The molecule factory of the future

self-assembling synthetic nanostructures

Munich, 11/13/2008

In the cell interior, enzymes spontaneously organise themselves into molecular factories which play a role in processes such as metabolism. Nature achieves this by using the basic principle of molecular self-assembly, which operates at the tiniest level and is extremely efficient. So how about utilising this principle to build our own ‘molecule factories’? A group of scientists in Munich, led by Professor Hermann Gaub, Chair of Applied Physics at Ludwig-Maximilians-University (LMU) München, have taken a crucial step towards this goal. Using an atomic force microscope, they are able to organise molecules into grids in defined structures to within just a few nanometres (millionths of a millimetre) in the laboratory. In a second step, these grids are then used as foundations for complex, self-assembling structures. One advantage of their technique is that it is possible to watch molecular assembly ‘live’, as it happens, allowing errors to be corrected immediately. (Nano Letters, November 12, 2008)

The assembly of individual molecules into complex structures within organisms usually takes place automatically without external agency. Some molecular building blocks have a kind of lock on the outside, to which other molecules possess the key. Building blocks which fit together join together automatically as soon as they meet. Complex structures are formed within cells by means of this self-assembling principle – indeed whole organisms are created in this way.

The physicists Elias Puchner and Stefan Kufer, at the Chair of Applied Physics at LMU Munich, have now utilised this principle to assemble nano-scale building blocks into complex patterns. The researchers have for some time been able to pick up molecules from a depot and place them at a specific position with nanometre precision using an atomic force microscope (AFM), in the same way as a builder uses a crane. The ‘hooks’ for the molecules are sections of DNA with ends of varying ‘stickiness’.

The group has now combined this method with the principle of self-organisation. Using an atomic force microscope, they first created a grid of biotin molecules. The next step consisted of using the biotin molecules as anchors for streptavidin molecules, which precisely bind to biotin in accordance with the lock and key principle. Their technique can be used to place any nano-scale building blocks at the positions defined by the biotin molecules.

To achieve this, all that’s required is that a streptavidin molecule is first attached to each of these building blocks. As soon as the streptavidin ‘key’ molecules approach the biotin positions, they will adopt the same pattern. “It’s as if, in order to build a castle, all you have to do is shake a heap of stone blocks onto a blueprint. The actual building work then occurs of its own accord,” explains Gaub.

His colleagues have succeeded in creating structures from a variety of nanocrystals using this method. One of the major benefits of this technology is that, according to Gaub, “If you want to construct functional nanosystems, a lot depends on precise positioning of the building blocks. With our technique, it is possible to observe the molecules ‘live’ during assembly, allowing any errors to be corrected immediately.”

Many novel applications could be conceived for this method. By stringing together specific enzymes, for example, it could in future be possible to build entire molecule factories. These might, for example, cleave cellulose-lignin complexes to generate energy. Such artificial enzyme complexes could allow plants which are not needed for food to be used to produce biofuels.

The research, which is published in the journal “Nano Letters”, was supported by the “Nanosystems Initiative Munich” (NIM) center of excellence and LMU’s “Functional NanoSystems” (FuNS) innovation programme.

Further material can be found at:
http://pubs.acs.org/cgi-bin/abstract.cgi/nalefd/asap/abs/nl8018627.html
A live film of superstructure assembly (quicktime) can be viewed at:
http://pubs.acs.org/subscribe/journals/nalefd/suppinfo/nl8018627/nl8018627-File003.qt

Publication:
“Nanoparticle Self-Assembly on a DNA-Scaffold Written by Single-Molecule Cut-and-Paste”,
Puchner, E. M.; Kufer, S. K.; Strackharn, M.; Stahl, S. W. and Gaub, H. E.
Nano Letters November 12, 2008

Contact:
Professor Dr. Hermann Gaub
Exzellenzcluster Nanosystems Initiative Munich (NIM) und Center for Nanoscience (CeNS) der LMU
Tel.: ++49 (0) 89 / 2180 – 3172
Fax: ++49 (0) 89 / 2180 – 2050
E-mail: gaub@physik.uni-muenchen.de
Internet: www.biophysik.physik.uni-muenchen.de

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