In the rapid and fast-growing world of nanotechnology,
researchers are continually on the lookout for new building blocks to
push innovation and discovery to scales much smaller than the tiniest
speck of dust.
In the Biodesign Institute at Arizona State University,
researchers are using DNA to make intricate nano-sized objects. Working
at this scale holds great potential for advancing medical and
electronic applications. DNA, often thought of as the molecule of life,
is an ideal building block for nanotechnology because they
self-assemble, snapping together into shapes based on natural chemical
rules of attraction. This is a major advantage for Biodesign
researchers like Hao Yan, who rely on the unique chemical and physical
properties of DNA to make their complex nanostructures.
While scientists are fully exploring the promise of DNA
nanotechnology, Biodesign Institute colleague John Chaput is working to
give researchers brand new materials to aid their designs. In an
article recently published in the Journal of the American Chemical
Society, Chaput and his research team have made the first
self-assembled nanostructures composed entirely of glycerol nucleic
acid (GNA)—a synthetic analog of DNA.
“Everyone in DNA nanotechnology is essentially
limited by what they can buy off the shelf,” said Chaput, who
is also an ASU assistant professor in the Department of Chemistry and
Biochemistry. “We wanted to build synthetic molecules that
assembled like DNA, but had additional properties not found in natural
DNA.”
The DNA helix is made up of just three simple parts: a sugar
and a phosphate molecule that form the backbone of the DNA ladder, and
one of four nitrogenous bases that make up the rungs. The nitrogenous
base pairing rules in the DNA chemical alphabet fold DNA into a variety
of useful shapes for nanotechnology, given that "A" can only form a
zipper-like chemical bond with "T" and "G" only pair with "C."
In the case of GNA, the sugar is the only difference with DNA.
The five carbon sugar commonly found in DNA, called deoxyribose, is
substituted by glycerol, which contains just three carbon atoms.
Chaput has had a long-standing interest in tinkering with
chemical building blocks used to make molecules like proteins and
nucleic acids that do not exist in nature. When it came time to
synthesize the first self-assembled GNA nanostructures, Chaput had to
go back to basics. “The idea behind the research was what to
start with a simple DNA nanostructure that we could just
mimic.”
The first self-assembled DNA nanostructure was made by Ned
Seeman’s lab at Columbia University in 1998, the very same
laboratory where ASU professor Hao Yan received his Ph.D.
Chaput’s team, which includes graduate students Richard Zhang
and Elizabeth McCullum were not only able to duplicate these
structures, but, unique to GNA, found they could make mirror image
nanostructures.
In nature, many molecules important to life like DNA and
proteins have evolved to exist only as right-handed. The GNA
structures, unlike DNA, turned out to be
‘enantiomeric’ molecules, which in chemical terms
means both left and right-handed.
“Making GNA is not tricky, it’s just three
steps, and with three carbon atoms, only one stereo center,”
said Chaput. “It allows us to make these right and
left-handed biomolecules. People have actually made left-handed DNA,
but it is a synthetic nightmare. To use it for DNA nanotechnology could
never work. It’s too high of a cost to make, so one could
never get enough material.”
The ability to make mirror image structures opens up new
possibilities for making nanostructures. The research team also found a
number of physical and chemical properties that were unique to GNA,
including having a higher tolerance to heat than DNA nanostructures.
Now, with a new material in hand, which Chaput dubs
‘unnatural nucleic acid nanostructures,’ the group
hopes to explore the limits on the topology and types of structure they
can make.
“We think we can take this as a basic building block
and begin to build more elaborate structures in 2-D and see them in
atomic force microscopy images,” said Chaput. “I
think it will be interesting to see where it will all go. Researchers
come up with all of these clever designs now.”
Posted 30th April 2008
