3D DNA-Directed Nanoassembly
If you're not satisfied with the materials provided by nature, why not build your own materials - from the atoms on up? Three-dimensional nanoassembly has now been accomplished by two different teams from Northwestern University and the Brookhaven National Laboratory.
"The crystal structures are deliberately designed," says Northwestern's Chad Mirkin, one of the materials scientists who pioneered DNA linking in the 1990s and a coauthor of one of today's reports. "This is a new way of making things."
Until now, attempts to program nanoparticle self-assembly in three dimensions has produced mostly disordered clumps. The two teams have overcome the problems involved by using longer DNA strands that give the particles more flexibility during crystal formation.
Here's how it works:
While the details of the Northwestern and Brookhaven systems differ, both pad out their DNA strands with sequences that act as spacers and flexors, in addition to complementary sequences on the DNA ends that bind particles together. The groups start by binding one of two types of DNA to gold nanoparticles. The DNA types are complementary to each other. These two pools of modified particles are then mixed and cooled. DNA strands with complementary DNA form a double helix, tying together their respective nanoparticles, while identical DNA strands act like springs to repel their respective particles. The spacers on each DNA strand, meanwhile, allow bound particles to twist and bend so each particle in the mix can bind the largest number of complementary particles.
The result is exactly what theory predicts: a crystal lattice in which each particle of one type is surrounded by eight of the others marking the corners of a cube.
(Gold nanoparticles programmed self-assembly
Sequences of DNA attached to gold nanoparticles (upper image) program the particles’ self-assembly into novel crystals (lower image). X-ray diffraction confirms the crystals--partly squashed by the electron microscopy that produced these images--to be perfect lattices of tens of thousands of particles.)
As far as I know, the first mention of trying to make something with individual atoms was in A Menace in Miniature, a 1937 story by early sf great Raymond Z. Gallun.
"With the Scarab as big as a beetle, I could make a Scarab as big as a sand grain. This second Scarab could build a miniature of itself, as big as a dust grain. The third Scarab could construct a fourth, bearing the same proportions as the first to the second, or the second to the third. And so on, down, to the limit imposed by the ultimate indivisibility of the atoms themselves."
(Read more about Gallun's ultra-microrobots)
While we're waiting for researchers to perfect self-assembly at the nano level, there are other methods. Nanoassembly can also be done by "hand" - or by "nanohand." Take a look at this remarkable video of a nanohand constructing a nanodevice with nanofibers.
From Researchers create three-dimensional structures using DNA-directed assembly via Smart Economy.
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