Protein Nanowires Made by Bacteria Show Potential in Developing Next Generation of Sustainable Electronics

Protein-based materials that demonstrate electronic conductivity allow the development of bioelectronic components and tools from sustainable and nontoxic materials. These materials are also well-suited to combine with biological systems for biosensor applications.

Potential of Proteins in Electronics

Harnessing proteins to deliver charge carriers shows potential in the development of ultra-low-power electrical units. This means that rendering protein components electronically conductive would benefit the fabrication of bioelectronic devices. Combining protein engineering and nanoelectronics holds promise for creating cutting-edge technologies which connect biological systems and electronic devices.

Aside from this, proteins can also be genetically engineered to make self-assembling nanostructured platforms that would allow the attachment and positioning of useful molecules with specific geometries. Engineering conductive protein scaffolds can be inspired by bacteria capable of transferring electrons over micrometer-scale distances.

Protein Nanowires for Power Harvesting

Electricity is generated by the movement of electrons between atoms. There are also events in nature which require this motion, such as photosynthesis. Meanwhile, naturally occurring bacteria use conductive filaments, called nanowires, to transfer electrons across their membranes. These bacterial nanowires can interact with biological systems and be used in biosensing.

However, these nanowires have limited functionality and are hard to modify when extracted directly from bacteria. To overcome this challenge, scientists from University of New South Wales genetically engineered a fiber using the bacteria Escherichia coli. The results of their study are discussed in the paper "Fabrication of Electronically Conductive Protein-Heme Nanowires for Power Harvesting."

Led by Dr. Lorenzo Travaglini, the research team modified the DNA of E. coli so they will only create the proteins they need to survive. They also engineered these microbes to build the specific proteins designed by the team.

By itself, the protein created by E. coli would not be highly conductive, so scientists would need to add a single ingredient. The missing component was identified as a heme molecule, a circular structure which contains an iron atom sitting in the middle. It is the one responsible for delivering oxygen in red blood cells from the lungs to the rest of the body.

Previous study revealed that heme molecules allow electron transfer when arranged closely together, so Dr. Travaglini and colleagues decided to integrate heme into the filaments created by the bacteria. The team suspected that the electrons could jump between heme molecules when arranged close enough together.

To measure the conductance of the engineered filaments, the experts laid a film of the material across an electrode and applied an electric potential. As expected, they discovered that the protein became conductive by adding heme to the filament, while the bare filament did not show electric current.

Dr. Travaglini and his team conducted more tests and discovered that the engineered filament was also responsive to humidity. They decided to make a simple humidity sensor to measure how the current responds to moisture in the air. By simply breathing onto the device, they found that each peak in the conductivity of the fiber corresponded to an exhale.

The researchers believe that their findings could pave the way for the development of protein-based, environmentally friendly and sustainable electrical components and devices. These could one day lead to innovations in biomedicine, energy harvesting, and environmental sensing.