Handling the molecules of life

Fabrication and assembly

March 4, 2008

Schematic of a single-molecule cut-and-paste event. (Courtesy of Hermann Gaub.)

In a move toward improved functional biomolecular assembly, an atomic force microscope (AFM) probe, modified with DNA ‘handles’ has been developed for the relocation of complimentary DNA strands [Kufer et al., Science (2008) 319, 594].

A team of US and German scientists use the DNA handles to hybridize to, unzip, and detach a single DNA strand from its compliment, located in a depot on a substrate surface.

The newly formed DNA unit, now attached to the AFM probe, can be moved to another site on the substrate where its free end can hybridize with a different, but complimentary DNA strand.

At this point, the DNA strand is still attached to the handle on the tip but is now paired with the strand attached to the substrate. As the probe is retracted from the surface a force gradually builds up within the two DNA duplexes caught in between the probe and the surface.

Rupture eventually occurs between the strands at the weakest point of the duplexes, the handle. The longer section of the DNA unit remains attached to the substrate while the handle, still covalently attached to the tip, is free to start the process again all over again. In contrast to dip-pen nanolithography, the DNA structures are assembled molecule-by-molecule.

Coauthor Hermann E. Gaub of the Ludwig-Maximilians-Universität in Germany has a clear view for the future of this cut-and-paste technique. “While we demonstrated this concept of serial assembly for one cantilever only, the rapid progress in parallel cantilever arrays, where each of the several thousand cantilevers is controlled individually, will allow the massively parallel assembly of new structures based on enzymes or functional nanoparticles with designed functions.”

Katerina Busuttil