I took a look at the full paper, which is, after all, in a very prestigious journal.
Here is the author's suggested mechanism for the observation:
We therefore propose the following qualitative mechanism for energy harvesting in the nanowire film. Water molecules in air naturally comprise ionized species25,26,27, or are ionized when adsorbed on the nanowire surface. The ionized clusters (for example, H(H2O)n+/HO(H2O)n? ) donate charge (for example, H+/e? ) to the nanowire, supplying the closed-loop current flow driven by the voltage resulting from the moisture gradient. A dynamic adsorption–desorption exchange of water molecules at the interface provides a continuous input. The ambient environment provides a large reservoir for this continuous exchange of water molecules to generate a sustained electric output (Fig. 1c). This mechanistic picture is consistent with previous findings of spontaneous surface charging on solid interfaces by atmospheric moisture25,26,27. Our nanowires seem to yield a particularly efficient charge transfer for continuous electric output, probably because of collective effects from surface groups with high affinity for water molecules and a self-maintained electric field that facilitates ionization and charge transfer. Future studies are required to determine the specific charge species and associated transfer processes.
The authors claim to show that their device depends very much on the presence of water vapor. The two references I accessed from this excerpt claimed similar
The preparative process for making this device is worth a look.
Synthesis and purification of protein nanowires
Geobacter sulfurreducens was routinely cultured at 25?°C under strict anaerobic conditions (80/20 N2/CO2) in chemostats34 in a previously described35 mineral-based medium containing acetate (15 mM) as the electron donor and fumarate (40 mM) as the electron acceptor. Cells were collected with centrifugation and resuspended in 150 mM ethanolamine buffer (pH 10.5). The nanowires were harvested and purified as described36. Briefly, protein nanowires were sheared from the cells in a blender. Cells were removed by centrifugation. The nanowires in the supernatant were precipitated with ammonium sulfate followed by centrifugation. The precipitate was resuspended in ethanolamine buffer and additional debris was removed by centrifugation. Nanowires were collected with a second 10% ammonium sulfate precipitation and subsequent centrifugation at 13,000g. The nanowires were resuspended in ethanolamine buffer. This nanowire preparation was dialysed against deionized water to remove the buffer and stored at 4?°C.
Fabrication of protein-nanowire devices
The bottom electrode (Cr/Au, 10/100 nm) was first defined on a glass slide (25 × 75 mm2; Fisher Scientific) by standard metal electron-beam evaporation using a shadow mask. A polydimethylsiloxane (PDMS, Sylgard 184, 10/1 mix ratio; Dow Corning) film (3–5 mm thick) was cut with an opening (1–25 mm2), which served as the well for holding the nanowire solution and placed on the glass slide with the opening aligned to the defined bottom electrode. The purified nanowire solution was tuned to pH 2.0 with hydrochloric acid (HCl) solution to improve nanowire conductivity37 and drop-casted into the PDMS well. Nanowire film prepared by as-purified, close-to-neutral solution without HCl yielded a similar electric output (Supplementary Fig. 19). The glass slide was then placed on a hot plate (at roughly 80?°C) to facilitate solvent (water) evaporation in order to form the nanowire thin film (Supplementary Fig. 1a). Note that the nanowires have been found to be stable at temperatures higher than 100?°C (ref. 16). The final nanowire-film thickness was controlled by tuning the solution volume over the unit area. Empirically, a 110 µl cm?2 nanowire solution (150 µg ml?1) yielded an average film thickness of roughly 1 µm. The PDMS mould was removed after nanowire-film assembly. Finally, a confined gold electrode was placed on top of the nanowire film to complete the device structure for electrical measurement. Two forms of top gold electrodes were used (Supplementary Fig. 1g). The first was a braided gold-plated shield (diameter roughly 0.7 mm, model CC-SC-50; LakeShore) and the second was a polyethylene terephthalate (PET) thin-film stripe (roughly 0.5 mm wide) coated with 50-nm gold film. Both top electrodes yielded close electrical outputs. For control protein-nanowire devices using printed carbon electrodes (Supplementary Fig. 4), conductive carbon film was printed using a desktop inkjet printer (DMP-2831, Dimatix; carbon ink JR-700HV, NovaCentrix) on the glass slide and on a paper stripe to form the bottom and top electrodes, respectively.
This is a lot of work to produce a tiny current.
The news item headline is very misleading in my opinion. These kinds of journalistic overstatements easily lead to magic thinking, some of which there is far too much in dire times. At least it contains links that ultimately lead to the full paper, although I suspect that most people don't bother to go that far. They rather think of magic.
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