Two-dimensional, "sheet-like" nanostructures are commonly employed in biological
systems such as cell membranes, and their unique properties have inspired interest
in materials such as graphene. Now, Berkeley
Lab scientists have made the largest two-dimensional polymer crystal self-assembled
in water to date. This entirely new material mirrors the structural complexity
of biological systems with the durable architecture needed for membranes or
integration into functional devices.
These self-assembling sheets are made of peptoids, engineered polymers that
can flex and fold like proteins while maintaining the robustness of manmade
materials. Each sheet is just two molecules thick yet hundreds of square micrometers
in area—akin to ‘molecular paper’ large enough to be visible
to the naked eye. What’s more, unlike a typical polymer, each building
block in a peptoid nanosheet is encoded with structural ‘marching orders’—suggesting
its properties can be precisely tailored to an application. For example, these
nanosheets could be used to control the flow of molecules, or serve as a platform
for chemical and biological detection.
"Our findings bridge the gap between natural biopolymers and their synthetic
counterparts, which is a fundamental problem in nanoscience," said Ronald
Zuckermann, Director of the Biological Nanostructures Facility at the Molecular
Foundry. "We can now translate fundamental sequence information from proteins
to a non-natural polymer, which results in a robust synthetic nanomaterial with
an atomically-defined structure."
The building blocks for peptoid polymers are cheap, readily available and generate
a high yield of product, providing a huge advantage over other synthesis techniques.
Zuckermann, instrumental in developing the Foundry’s one-of-a-kind robotic
synthesis capabilities, worked with his team of coauthors to form libraries
of peptoid materials. After screening many candidates, the team landed upon
the unique combination of polymer building blocks that spontaneously formed
peptoid nanosheets in water.
Zuckermann and coauthor Christian Kisielowski reached another first by using
the TEAM 0.5 microscope at the National Center for Electron Microscopy (NCEM)
to observe individual polymer chains within the peptoid material, confirming
the precise ordering of these chains into sheets and their unprecedented stability
while being bombarded with electrons during imaging.
"The design of nature-inspired, functional polymers that can be assembled
into membranes of large lateral dimensions marks a new chapter for materials
synthesis with direct impact on Berkeley Lab’s strategically relevant
initiatives such as the Helios project or Carbon Cycle 2.0," said NCEM’s
Kisielowski. "The scientific possibilities that come with this achievement
challenge our imagination, and will also help move electron microscopy toward
direct imaging of soft materials."
"This new material is a remarkable example of molecular biomimicry on
many levels, and will no doubt lead to many applications in device fabrication,
nanoscale synthesis and imaging," Zuckermann added.
This research is reported in a paper titled, "Free floating ultra-thin
two-dimensional crystals from sequence-specific peptoid polymers," appearing
in the journal Nature Materials and available in Nature Materials online. Co-authoring
the paper with Zuckermann and Kisielowski were Ki Tae Nam, Sarah Shelby, Phillip
Choi, Amanda Marciel, Ritchie Chen, Li Tan, Tammy Chu, Ryan Mesch, Byoung-Chul
Lee and Michael Connolly.
This work at the Molecular Foundry was supported by DOE’s Office of Science
and the Defense Threat Reduction Agency.