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In
recent years, scientists have begun to harness DNA’s powerful molecular
machinery to build artificial structures at the nanoscale using the
natural ability of pairs of DNA molecules to assemble into complex
structures. Such “DNA origami,” first developed at the California
Institute of Technology,* could provide a means of assembling complex
nanostructures such as semiconductor devices, sensors and drug delivery
systems, from the bottom up.
While
most researchers in the field are working to demonstrate what’s
possible, scientists at the National Institute of Standards and
Technology (NIST) are seeking to determine what’s practical.
According
to NIST researcher Alex Liddle, it’s a lot like building with
LEGOs—some patterns enable the blocks to fit together snugly and stick
together strongly and some don’t.
“If
the technology is actually going to be useful, you have to figure out
how well it works,” says Liddle. “We have determined what a number of
the critical factors are for the specific case of assembling
nanostructures using a DNA-origami template and have shown how proper
design of the desired nanostructures is essential to achieving good
yield, moving, we hope, the technology a step forward.”
In
DNA origami, researchers lay down a long thread of DNA and attach
“staples” comprised of complementary strands that bind to make the DNA
fold up into various shapes, including rectangles, squares and
triangles. The shapes serve as a template onto which nanoscale objects
such as nanoparticles and quantum dots can be attached using strings of
linker molecules.
The
NIST researchers measured how quickly nanoscale structures can be
assembled using this technique, how precise the assembly process is, how
closely they can be spaced, and the strength of the bonds between the
nanoparticles and the DNA origami template.
What
they found is that a simple structure, four quantum dots at the corners
of a 70-nm by 100-nm origami rectangle, takes up to 24 hours to
self-assemble with an error rate of about 5%.
Other
patterns that placed three and four dots in a line through the middle
of the origami template were increasingly error prone. Sheathing the
dots in biomaterials, a necessity for attaching them to the template,
increases their effective diameter. A wider effective diameter (about 20
nm) limits how closely the dots can be positioned and also increases
their tendency to interfere with one another during self-assembly,
leading to higher error rates and lower bonding strength. This trend was
especially pronounced for the four-dot patterns.
“Overall,
we think that this process is good for building structures for
biological applications like sensors and drug delivery, but it might be a
bit of a stretch when applied to semiconductor device manufacturing—the
distances can’t be made small enough and the error rate is just too
high,” says Liddle.
Nanomanufacturing with DNA origami: factors affecting the kinetics and yield of quantum dot binding.
