Squid-inspired Proteins can Function as Programmable Assemblers of 2D Materials

Squid-inspired proteins can be used as programmable assemblers of 2D materials, like graphene oxide, to develop hybrid materials with minute spacing between layers appropriate for high-efficiency devices including mechanical actuators, energy storage systems and flexible electronics, according to an interdisciplinary group of Penn State Researchers.

2D layered materials can be made by vacuum (chemical vapor) deposition. But the process is expensive and takes a long time. With chemical vapor deposition the problem also is we can't scale up.

Melik C. Demirel, Pierce Development Professor and Professor of Engineering Science and Mechanics

Materials like graphene oxide are made up of single layers of molecules connected in a plain. The height is only that of one molecule, whereas the breadth and length of the sheet can be anything. In order to make usable composites and devices, 2D materials have to be stacked either in loads of identical sheets or combinations of sheets of various composition stacked to specification. Along with Mauricio Terrones, Professor of Physics, Chemistry and Materials Science and Engineering, and Director of 2D Atomic Center, Penn State, Demirel and his group are currently exploring stacking sheets of identical materials using a solvent method that self assembles.

Using the solvent approach the molecules are self-assembling, self-healing and flexible. Currently we are stacking identical layers, but they don't have to be the same.

Melik C. Demirel, Pierce Development Professor and Professor of Engineering Science and Mechanics

To make these molecular composites using solvent technology, the Researchers combined sheets of graphene oxide with synthetic polymers patterned after proteins identified in squid ring teeth. One end of the protein strand is attached to the edge of a graphene oxide sheet, while the other end is attached to the edge of another graphene dioxide sheet. The graphene oxide sheets self-assemble to stack up with proteins connecting the edges of the sheets. The length of these tandem-repeat proteins, their molecular weight, helps determines the distance between sheets.

Up until now, no one has been able to stack composite layers closer than 1 nanometer. We can stack them at atomistic precision with 0.4, 0.6 or 0.9 nanometer resolution by choosing the right molecular weight of the same protein. Respectively.

Melik C. Demirel, Pierce Development Professor and Professor of Engineering Science and Mechanics

The Researchers tested the ability of this material in order to make minute devices by creating bimorph thermal actuators. A bimorph activator is a tiny piece of material prepared from two different layers and positioned perpendicular to a surface. The bimorph actuator bends from the perpendicular when activated by an electric current.

The Researchers report in the July issue of Carbon that, "these novel molecular composite bimorph actuators can facilitate thermal actuation at voltages as low as about 2 volts, and they boast energy efficiencies 18 times better than regular bimorph actuators assembled using bulk graphene oxide and tandem repeat films." They consider that higher molecular weight proteins can reach much higher displacements.

Other Researchers on this project, all from Penn State, include Mert Vural, Post-Doctoral Fellow; Abdon Pena-Francesch, Graduate Student; and Huihun Jung, Graduate Student, all in Engineering Science and Mechanics; Yu lei, Graduate Student in Physics; and Benjamin Allen, Research Associate, the Huck Institutes of Life Sciences and biochemistry and molecular biology.

The U.S. Army Research Office funded this work.

Video shows layered, self-assembled graphene oxide sheets with synthetic proteins patterned on squid ring teeth made into an actuator with substantial curvature. The second segment shows the same device using graphene oxide only. There is no movement. Credit: Melik Demirel / Penn State