Hard-Wired Solid-State Bioelectronic Micropore Devices: Permanent Metal-Protein-Metal Junction Proof-of-Concept.

The design, fabrication, and application of robust metal/protein/metal junctions are presented with ultrathin (≈20 nm) protein films demonstrating long-term stability in ambient conditions and preserving their electron transport behavior also at ≈10 K. These junctions establish a reliable platform with a permanent contact configuration, where the confined protein layer retains its functional activity after metal contact evaporation on the protein. A bottom-up micropore device (MpD) fabrication strategy is used and optimized to ensure reproducibility. The sub-nanometer roughness of the bottom electrode is preserved within the micropore, enabling uniform protein layer deposition and film formation. In the MpD structures, protein layers are integrated between Au-covered substrates and an e-beam evaporated Pd contacts. Depositing multi-layered protein films allows for defining film widths, as tested by the atomic force microscopy (AFM)-based scratching technique. The films are composed of human serum albumin (HSA) and bacteriorhodopsin (bR). Pd's preferred 2D growth minimized metal penetration and short circuits. Impedance phase response analysis shows that ≈60% of the junctions are functional ones, demonstrating the effectiveness of the fabrication approach. These protein-based MpD junctions provide a basis for future stable platforms for electron transport studies of bio- and other soft materials.