The team at Stevens Institute of Technology achieved this by covering a white button mushroom with 3D-printed clusters of cyanobacteria that generate electricity and graphene nanoribbons that collect the current.
The work, reported in Nano Letters, is part of a broader effort to understand and utilise the biological machinery of cells in order to fabricate new technologies.
"In this case, our system - this bionic mushroom - produces electricity," said Manu Mannoor, an assistant professor of mechanical engineering at Stevens. "By integrating cyanobacteria that can produce electricity, with nanoscale materials capable of collecting the current, we were able to better access the unique properties of both, augment them, and create an entirely new functional bionic system."
White button mushrooms host a rich microbiota but not cyanobacteria specifically, prompting Mannoor and postdoctoral fellow Sudeep Joshi, to ask if agaricus bisporus could provide the nutrients, moisture, pH and temperature for the cyanobacteria to produce electricity for a longer period.
Mannoor and Joshi showed that the cyanobacterial cells lasted several days longer when placed on the cap of a white button mushroom compared to silicone and dead mushrooms used as controls.
"The mushrooms essentially serve as a suitable environmental substrate with advanced functionality of nourishing the energy-producing cyanobacteria," said Joshi. "We showed for the first time that a hybrid system can incorporate an artificial collaboration, or engineered symbiosis, between two different microbiological kingdoms."
Mannoor and Joshi first 3D-printed an "electronic ink" containing the graphene nanoribbons to form a branched network that collects electricity.
They then printed a" bio-ink" containing cyanobacteria onto the mushroom's cap in a spiral pattern intersecting with the electronic ink. At these locations, electrons could transfer through the outer membranes of the cyanobacteria to the conductive network of graphene nanoribbons. Shining a light on the mushrooms activated cyanobacterial photosynthesis, generating a photocurrent.
In addition to the cyanobacteria living longer in a state of engineered symbiosis, Mannoor and Joshi showed that the amount of electricity these bacteria produce can vary depending on the density and alignment with which they are packed: the more densely packed together they are, the more electricity they produce. With 3D printing, it was possible to assemble them to boost their electricity-producing activity eight-fold.
"With this work, we can imagine enormous opportunities for next-generation bio-hybrid applications," Mannoor said. "For example, some bacteria can glow, while others sense toxins or produce fuel. By seamlessly integrating these microbes with nanomaterials, we could potentially realise many other amazing designer bio-hybrids for the environment, defence, healthcare and many other fields."
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