Electrically conductive protein nanowires made by the microbe Geobacter sulfurreducens can generate an electric current simply by absorbing atmospheric moisture, according to researchers at the University of Massachusetts Amherst. [Liu, X. et al., Nature (2020); DOI: 10.1038/s41586-020-2010-9]

You might say that the "Air-gen" device being pioneered by Yun Lao and Derek Lovley and their teams makes electricity out of thin air. He suggests that in his thirty years or research on such material, this is perhaps "the most amazing and exciting application of protein nanowires yet".

Yao's new technology opens up the possibility of a non-polluting, renewable and low-cost method of electricity generation that works even where humidity is very low such as hot deserts. Moreover, unlike solar it functions in the dark and unlike wind power it works when the air is still. More to the point, it works indoors offering the possibility of small-scale domestic or even industrial power generation.

A thin film of patterned protein nanowires, just 7 micrometers thick sits on a gold electrode and a second, smaller gold electrode covers part of the upper surface. Water vapor is adsorbed by the proteins and in the fine pores between the nanowires an electrical current is established that flows from one electrode to the other. The device operates with a sustained voltage of about 0.5 volts and the current is 17 microamps per square centimeter, this is sustained for around 20 hours before the device has to refresh itself. Earlier technology in this area has to self-recharge on a shorter lifetime than the generation cycle, producing only very short bursts of energy at much lower current density. The present device could be used to power small electronics and wearable technology, such as health and fitness monitors.

"The ultimate goal is to make large-scale systems. For example, the technology might be incorporated into wall paint that could help power your home. Or, we may develop stand-alone air-powered generators that supply electricity off the grid. Once we get to an industrial scale for wire production, I fully expect that we can make large systems that will make a major contribution to sustainable energy production," Yao said.

It was Lovley that discovered Geobacter in the mud of the Potomac River thirty years ago and suspected its unique characteristics might be useful. However, now that they know about the proteins it makes, his lab, plans to engineer novel microbial strains that can make the protein nanowires more quickly, more efficiently, and at lower cost. They have already succeeded in making the well-known "lab" microbe Escherichia coli into a protein nanowire factory by splicing in the requisite Geobacter genes. Such a development would remove one of the bottlenecks opening up rapid development of the technology, allowing them to mass produce the protein nanowires through fermentation using established E. coli technology.