Abstract
<jats:p>A defining feature of electron transport, ETp, through protein films is its remarkably weak temperature dependence, even over distances (15–35 nm) that far exceed the range predicted for coherent tunneling. We measure ETp across multilayer films of human serum albumin (HSA) and bacteriorhodopsin (bR) using Au/protein/Pd micropore (MpD) junctions with negligible contact resistance. Both proteins show stable current–voltage characteristics that are essentially temperature-independent from 0.2 to 300 K at applied biases from ±0.05 to ±1 V. These results exclude thermally activated hopping. The ~2 eV HOMO–LUMO gap and the absence of detectable electronic states near the electrode Fermi level rule out resonant transport. Time-dependent, voltagepulse, and impedance measurements exclude ionic conduction or interfacial artifacts. Together, these findings show that the experimentally observed ETp type is intrinsic to the proteins. The consistency of these findings across two structurally and functionally distinct proteins suggests that long-range temperature-independent ETp is a general property of dry protein films, arising from their collective electrical architecture, including peptide backbones, hydrogen-bond networks, structurally bound water (retained in the dry films), and electronic polarization. Together, these create a responsive three-dimensional environment capable of supporting long-range electron transport beyond the scope of conventional molecular electronics models.</jats:p>