2D Silk Protein Layers on Graphene Pave the Way for Advanced Microelectronics and Computing

After thousands of years of value, silk continues to surprise. It could now open a whole new avenue for microelectronics and computing.

Although silk protein has been used in electronics design, its use is currently limited in part because silk fibers are a messy tangle of spaghetti-like strands.

Now, a research team led by scientists at the Department of Energy’s Pacific Northwest National Laboratory has managed to get a handle on the problem. They report in the journal Scientific progress that they obtained a uniform two-dimensional (2D) layer of silk protein fragments, or “fibroins,” on graphene, a carbon-based material useful for its excellent electrical conductivity.

“These results provide a reproducible method for silk protein self-assembly, which is essential for the design and fabrication of silk-based electronic components,” said Chenyang Shi, lead author of the study. “Importantly, this system is nontoxic and water-based, which is crucial for biocompatibility.”

This combination of materials, silk on graphene, could form a sensitive, tunable transistor that is highly sought after by the microelectronics industry for wearable and implantable health sensors. The PNNL team also sees potential for their use as a key component of memory transistors, or “memristors,” in computer neural networks. Memristors, used in neural networks, allow computers to mimic the functioning of the human brain.

The Silk Road

For centuries, silkworm silk production was a closely guarded secret in China, while its fame spread along the famous silk trade routes to India, the Middle East, and eventually Europe. By the Middle Ages, silk had become a status symbol and a coveted commodity in European markets. Even today, silk is associated with luxury and status.

The same underlying properties that make silk fabric world-renowned (elasticity, durability and strength) have led to its use in advanced materials applications.

“There has been a lot of research on silk as a way to modulate electronic signals, but because silk proteins are naturally disordered, there is only a certain degree of control possible,” said James De Yoreo, a Battelle Fellow at PNNL and dual-appointed professor of materials science and engineering and chemistry at the University of Washington.

“So, with our experience in controlling the growth of materials on surfaces, we thought, ‘What if we could create a better interface?'”

To do this, the team carefully controlled the reaction conditions, adding individual silk fibers to the water-based system in precise ways. Using precise laboratory conditions, the team obtained a highly organized 2D layer of proteins packed into precise parallel β-sheets, one of the most common protein shapes in nature.

Further imaging studies and theoretical calculations showed that the thin silk layer adopts a stable structure with characteristics found in natural silk. An electronic structure at this scale – less than half the thickness of a DNA strand – supports the miniaturization found throughout the bioelectronics industry.

“This type of material lends itself to what we call field effects,” De Yoreo explains. “That means it’s a transistor that turns on or off in response to a signal. If you add, for example, an antibody, then when a target protein binds, you make a transistor change state.”

In fact, the researchers plan to use this starting material and technique to create their own artificial silk by adding functional proteins to improve its usefulness and specificity.

This study represents the first step in controlled silk lamination on functional electronic components. Key future research areas include improving the stability and conductivity of silk integrated circuits and exploring the potential of silk in biodegradable electronics to increase the use of green chemistry in electronics manufacturing.