"Miracle material" graphene Flexible circuits made of silk and graphene

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By controlling the nanostructure of silk proteins for the first time, scientists at the Pacific Northwest National Laboratory are paving the way for advanced microelectronic and computer-based applications.

Silk, a raw material with a long history, could soon revolutionize microelectronics. While silk proteins have already been used in designer electronics, their application was previously limited by their unstructured form. A research team from the Pacific Northwest National Laboratory (PNNL) has now developed a uniform two-dimensional layer of silk protein fragments on the conductive material graphene, as reported in the journal 'Science Advances'. This could open up new possibilities for electronics.

Self-assembly of silk proteins

"The results provide a reproducible method for the self-assembly of silk proteins, which is essential for the development and manufacture of silk-based electronics," said Chenyang Shi, the lead author of the study. "It is important to note that this system is non-toxic and water-based, which is crucial for biocompatibility."

The material combination, silk on graphene, could form a sensitive, tunable transistor that is urgently needed by the microelectronics industry for wearable and implantable sensors. The PNNL team also sees potential for their use as a key component of memory transistors or memristors in neural computing networks. Memristors enable computers to mimic the operation of the human brain.

The Silk Road

For centuries, the production of silkworm silk was a closely guarded secret in China, while its fame spread along the famed trade routes of the Silk Road to India, the Middle East, and eventually Europe. In the Middle Ages, silk became a status symbol and a sought-after commodity in European markets. Even today, silk is still associated with luxury and status.

The same fundamental properties that make silk fabric world-renowned—elasticity, durability, and strength—have led to its use in modern material applications. "There has been a lot of research with silk to modulate electronic signals, but since silk proteins are naturally disordered, only limited control was possible," said James De Yoreo, Battelle Fellow at PNNL and Professor of Materials Science and Engineering as well as Chemistry at the University of Washington.

"With our expertise in controlling material growth on surfaces, we thought, 'What if we could create a better interface?'" To this end, the team carefully controlled the reaction conditions and added individual silk fibers to the water-based system in a precise manner. Through meticulous laboratory conditions, the team achieved a highly organized 2D layer of proteins packed into precisely parallel β-sheets, one of the most common protein structures in nature.

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

"This type of material is suitable for what we call field effects," said De Yoreo. "This means that it acts as a transistor switch that turns on or off in response to a signal. For example, if you add an antibody and it binds to a target protein, the transistor switches its state." Indeed, the researchers plan to use this base material and technique to create their own synthetic silk, to which functional proteins will be added to enhance its usefulness and specificity.

Circuits integrated into silk

This study is the first step toward the controlled application of silk onto functional electronic components. Key areas of future research include improving the stability and conductivity of circuits integrated into silk and exploring the potential of silk in biodegradable electronics, aiming to increase the use of green chemistry in electronics manufacturing.

In addition to De Yoreo, the co-authors of the study included PNNL materials scientist Shuai Zhang and Xiang Yang Liu from Xiamen University, China. Other authors are Marlo Zorman from the University of Washington, Seattle, Xiao Zhao and Miquel B. Salmeron from the Lawrence Berkeley National Laboratory, and Jim Pfaendtner from North Carolina State University. (sb)