With growing interest in using nanoparticles for everything from
antibacterial socks to medical imaging to electronic devices, the need
to understand the environmental, health and safety risks of these
particles also grows. Researchers at the National Institute of Standards
and Technology (NIST) have developed a simple process for producing
nanocrystals that will enable studies of certain physical and chemical
properties that affect how nanoparticles interact with the world around
them.
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These electron microscope images show perfect-edged nanocubes Credit: NIST |
Because nanoparticles behave differently from bulk samples of the
same material, new tests to understand how they affect biological
systems must be developed. Toxicologists determine the hazards posed by
nanoparticles by introducing them to a biological system and monitoring
the effects, but they currently lack a set of control particles whose
size, shape and composition have been carefully produced and
characterized.
In a recent paper published in Angewandte Chemie,* NIST
scientists describe a one-step process that allows them to control the
size, shape and composition of gold-copper alloy nanocrystals to create
perfect-edged nanocubes as small as 3.4 nanometers—just half the
thickness of a cell wall and on the same size range as DNA.
The researchers combined and heated gold and copper precursors with
other chemicals to produce highly crystalline, homogeneous, perfect
nanocubes with abundant yield. To study the formation process, they
removed samples at 1 hour, 1.5 hours, 5 hours, and 24 hours and found
that just five hours were needed to produce perfectly cubic
nanoparticles of uniform size. By adjusting the ratios of the chemicals
in the original solution and the reaction time, they were able to
precisely control the size, shape and composition of the nanocubes. This
process is unique in allowing control of the ratio of copper to gold
atoms within the nanocube to either 3:1 or 1:3.
"It's a simple process, and to the best of our knowledge is the first
to use synthetic chemistry, or 'bottom up' technology, to produce
gold-containing nanocubes below 5 nanometers. Anything less than 10
nanometers has been extremely challenging due to the mobile behavior of
the gold atoms," says NIST physicist Angela R. Hight Walker, who wrote
the paper with Yonglin Liu, a guest researcher at NIST.
The NIST-developed process for creating such nanocubes will allow
toxicologists to systematically alter one of the nanocubes'
characteristics and observe how the change affects the biological
response, if at all.
This synthesis and the resulting high-quality nanocubes may have
other applications in areas such as solar energy, says Liu. "Typically,
we cannot make big batches of high-quality samples for testing; now we
can."
The perfect-edged nanocubes are unique from other nanocubes in the
literature, says Hight Walker. The sharp edges, as opposed to truncated
or rounded edges, will enable different, more reactive chemistry that
could be beneficial in applications such as catalysis—in which the
nanocubes would be used to initiate or enhance a chemical reaction.
*Y. Liu and A.R. Hight Walker. Monodisperse gold-copper bimetallic
nanocubes: facile one-step synthesis with controllable size and
composition. Angewandte Chemie. Posted online Aug. 16, 2010.
Media Contact: Jennifer Huergo, jennifer.huergo@nist.gov, 301-975-6343
