Berkeley Lab scientists have developed a nanoscale rope that braids itself, as seen in this atomic force microscopy image of the structure at a resolution of one-millionth of a meter.
Scientists at the U.S. Department of Energy’s Lawrence
Berkeley National Laboratory have coaxed polymers to braid themselves into
wispy nanoscale ropes that approach the structural complexity of biological
Their work is the latest development in the push to develop
self-assembling nanoscale materials that mimic the intricacy and functionality
of nature’s handiwork, but which are rugged enough to withstand harsh
conditions such as heat and dryness.
Although still early in the development stage, their
research could lead to new applications that combine the best of both worlds.
Perhaps they’ll be used as scaffolds to guide the construction of nanoscale
wires and other structures. Or perhaps they’ll be used to develop drug-delivery
vehicles that target disease at the molecular scale, or to develop molecular
sensors and sieve-like devices that separate molecules from one another.
Specifically, the scientists created the conditions for
synthetic polymers called polypeptoids to assemble themselves into ever more
complicated structures: first into sheets, then into stacks of sheets, which in
turn roll up into double helices that resemble a rope measuring only 600 nm in
“This hierarchichal self assembly is the hallmark of
biological materials such as collagen, but designing synthetic structures that
do this has been a major challenge,” says Ron Zuckermann, who is the Facility
Director of the Biological Nanostructures Facility in Berkeley Lab’s Molecular
In addition, unlike normal polymers, the scientists can
control the atom-by-atom makeup of the ropy structures. They can also engineer
helices of specific lengths and sequences. This “tunability” opens the door for
the development of synthetic structures that mimic biological materials’
ability to carry out incredible feats of precision, such as homing in on
“Nature uses exact length and sequence to develop highly
functional structures. An antibody can recognize one form of a protein over
another, and we’re trying to mimic this,” adds Zuckermann.
From left, Rachel Segalman, Hannah Murnen, and
Zuckermann and colleagues conducted the research at The
Molecular Foundry, which is one of the five DOE Nanoscale Science Research
Centers premier national user facilities for interdisciplinary research at the
nanoscale. Joining him were fellow Berkeley Lab scientists Hannah Murnen,
Adrianne Rosales, Jonathan Jaworski, and Rachel Segalman. Their research was
published in a recent issue of the Journal of the American Chemical Society.
The scientists worked with chains of bioinspired polymers
called a peptoids. Instead of using peptides to build proteins, however, the
scientists are striving to use peptoids to build synthetic structures that
behave like proteins.
The team started with a block copolymer, which is a polymer
composed of two or more different monomers.
“Simple block copolymers self assemble into nanoscale
structures, but we wanted to see how the detailed sequence and functionality of
bioinspired units could be used to make more complicated structures,” says
Rachel Segalman, a faculty scientist at Berkeley Lab and professor of Chemical
and Biomolecular Engineering at Univ.
of California, Berkeley.
With this in mind, the peptoid pieces were robotically
synthesized, processed, and then added to a solution that fosters self
The result was a variety of self-made shapes and structures,
with the braided helices being the most intriguing. The hierarchical structure
of the helix, and its ability to be manipulated atom-by-atom, means that it
could be used as a template for mineralizing complex structures on a nanometer
“The idea is to assemble structurally complex structures at
the nanometer scale with minimal input,” says Hannah Murnen. She adds that the
scientists next hope is to capitalize on the fact that they have minute control
over the structure’s sequence, and explore how very small chemical changes
alter the helical structure.
Says Zuckermann, “These braided helices are one of the first
forays into making atomically defined block copolymers. The idea is to take
something we normally think of as plastic, and enable it to adopt structures
that are more complex and capable of higher function, such as molecular
recognition, which is what proteins do really well.”
X-ray diffraction experiments used to characterize the
structures were conducted at beamlines 8.3.1 and 7.3.3 of Berkeley Lab’s
Advanced Light Source, a national user facility that generates intense x-rays
to probe the fundamental properties of substances. This work was supported in
part by the Office of Naval Research.