Fig. 3: Conducting filament and switching dynamics.

a SEM images of a protein-nanowire device (I) before, (II) after electroforming, and (III) after removal of the protein nanowires with ultrasonication. Scale bars, 100 nm. b FTIR spectra of a protein-nanowire film (~200 nm thick) at relative humidity (RH) of 0% (gray), 35% (red), 50% (blue), 65% (green), 80% (purple) and 100% (yellow). The broad peaks ~3400 cm⁻¹ correspond to O-H stretching band in free water⁴². The increased intensity indicates increased water adsorption in the film at higher RH. The increased intensities in other amide peaks could be caused by protein segments that became more mobile after moisture filling interstitial voids. c Average turn-on voltage (V_th) from devices (N = 12) in different RH. The error bars represent the standard deviation (s.d.). d Cyclic voltammetry curves using protein-nanowire coated Au cathode (blue) and SiO₂-coated Au cathode (red) in Ag⁺ (5 mM) solution at a rate of 25 mV·s⁻¹. The background curve (gray) was performed without Ag⁺. The onset reduction potential shows a right shift (black arrow) from ~0.25 V to ~0.35 V when switching from SiO₂ coating to protein-nanowire coating in the Au cathode, whereas the oxidation peak (~0.43 V) does not shift.