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NYU researchers create method
to precisely glue particles together on the micro- and nano-scale
RNCOS
January 17, 2009
Researchers at New York University have created a method to
precisely bind nano- and micrometer-sized particles together
into larger-scale structures with useful materials
properties. Their work, which appears in the latest issue of
the journal Nature Materials, overcomes the problem of
uncontrollable sticking, which had been a barrier to the
successful creation of stable microscopic and macroscopic
structures with a sophisticated architecture. |
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The long-term goal of the NYU researchers is
to create non-biological materials that have the ability to
self-replicate. In the process of self-replication, the
number of objects doubles every cycle. This exponential
growth stands in sharp contrast to conventional materials
production, where doubling the amount of product requires
twice the production time. At present, this linear scaling
poses a major stumbling block for the fabrication of useful
quantities of microscopic objects with a sophisticated
architecture, which are needed for the next stages of micro-
and nanotechnology.
In order to obtain self-replication, the researchers coat
micrometer-sized particles with short stretches of DNA,
so-called "sticky ends". Each sticky end consists of a
particular sequence of DNA building blocks and sticky ends
with complementary sequences form very specific bonds that
are reversible. Below a certain temperature, the particles
recognize each other and bind together, while they unbind
again above that temperature. This enables a scheme in which
the particles spontaneously organize into an exact copy on
top of a template, which can then be released by elevating
the temperature.
Scientists have used DNA-mediated interactions before, but
it has always been very difficult to bind only a subset of
particles—usually, either all particles or no particles are
bound. This makes it challenging to make well-defined
structures. Therefore, the NYU team, comprised of
researchers in the Physics Department's Center for Soft
Matter Research and in the university's Department of
Chemistry, sought to find a method to better control the
interactions and organization of the particles.
To do so, the researchers took advantage of the ability of
certain DNA sequences to fold into a hairpin-like structure
or to bind to neighboring sticky ends on the same particle.
They found that if they lowered the temperature very
rapidly, these sticky ends fold up on the particle—before
they can bind to sticky ends on other particles. The
particles stuck only when they were held together for
several minutes—a sufficient period for the sticky ends to
find a binding partner on another particle.
"We can finely tune and even switch off the attractions
between particles, rendering them inert unless they are
heated or held together—like a nano-contact glue," said
Mirjam Leunissen, a post-doctoral fellow in the Center for
Soft Matter Research and the study's lead author.
To maneuver the particles, the team used optical traps, or
tweezers. This tool, created by David Grier, chair of NYU's
Department of Physics and one of the paper's authors, uses
laser beams to move objects as small as a few nanometers, or
one-billionth of a meter.
The work has a range of possible applications. Notably,
because the size of micrometer-scale particles—approximately
one-tenth the thickness of a strand of human hair—is
comparable to the wavelength of visible light, ordered
arrays of these particles can be used for optical devices.
These include sensors and photonic crystals that can switch
light analogous to the way semi-conductors switch electrical
currents. Moreover, the same organizational principles apply
to smaller nanoparticles, which possess a wide range of
electrical, optical, and magnetic properties that are useful
for applications.
The work was supported by the National Science Foundation's
Materials Research Science and Engineering Center (MRSEC)
program, the Keck Foundation, and the Netherlands
Organization for Scientific Research.
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