Figure 1. Self-replicating DNA tiles
At low temperatures X' and Y' DNA tiles from the surrounding solution spontaneously bond to the complementary X and Y tiles in the initial structure. At higher temperatures the daughter copy thus formed lets go of the initial structure and the process subsequently repeats itself.
Figure 2. Self-replicating materials of micrometre or nanometre-sized building blocks
The new self-replication process could make the manufacturing of materials constructed from micrometre or nanometre-sized building blocks far more efficient, as only a single initial structure is needed which subsequently keeps on doubling in number. An exponential production rate is therefore achieved.
In the natural world self-replication is ubiquitous: minuscule building blocks in living entities replicate spontaneously and organise themselves into more complex structures. Artificial self-replication of non-living materials is extremely difficult, however. Up until now this was only possible for very specific structures. The researchers, including AMOLF group leader Mirjam Leunissen, have now made the first step towards a general process for the self-replication of a wide range of structures with various shapes and functions.
The researchers used artificial structures of DNA - so-called DNA tiles - dissolved in water to demonstrate the new process. These tiles are several tens of nanometres in size and consist of compactly folded DNA strands, from which four loose ends with a specific sequence of the bases A, C, G and T protrude. Like a barcode, these sticky ends determine the identity of a tile and ensure that tiles with complementary ends attach to each other: A always adheres to T, and C to G. When joined, the ends of the two tiles together form the characteristic double helix structure.
The researchers arranged seven tiles with two different identities (for example indicated with the letters X and Y) to form the ‘word’ X-Y-Y-X-Y-X-Y. Subsequently, tiles with complementary sticky ends, X' and Y', spontaneously attached themselves in the right order to this initial structure (X'-Y'-Y'-X'-Y'-X'-Y'). The sticky ends only stick at a lower temperature and so the 'daughter word' was separated from the initial structure by briefly increasing the temperature. After this the researchers repeated the process with the remaining separate tiles until these formed 'granddaughters' with exactly the same XY sequence of letters (See Figure 1).
This new replication process is an important step forward, as complex structures and the information enclosed in those are copied exactly. Despite using DNA, this new process is not the same as DNA copying in the cell, as no special biological machinery, such as enzymes, is used. In fact, even the DNA is synthetic, which makes the process highly robust. And best of all, the sticky DNA ends can not only be attached to DNA tiles but can also be placed on particles from a range of other materials, such as metal nanoparticles. This could make the manufacturing of new materials constructed from such building blocks far more efficient. Only one initial structure would have to be made and after that in each cycle the amount produced is doubled, which means that an exponential production rate is achieved.
The research was financed by the W.M. Keck Foundation, the National Science Foundation, the National institute of General Medical Sciences, the Army Research Office, NASA, the Office of Naval Research and the Netherlands Organisation for Scientific Research (NWO).
Dr. Mirjam Leunissen
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Self-Replication of Information-Bearing Nanoscale Patterns
Tong Wang, Ruojie Sha, Rémi Dreyfus, Mirjam E. Leunissen, Corinna Maass, David J. Pine, Paul M. Chaikin, and Nadrian C. Seeman
Nature (2011), DOI: 10.1038/nature10500