We used two different types of proteins, a globular one, human serum albumin (HSA), and a membrane one, bacteriorhodopsin (bR), to prepare the junctions. The micropore electrode was initially cleaned through sequential solvent sonication for 3 minutes each in acetone, isopropanol (IPA), and Milli-Q water. Subsequently, the bottom gold (Au) surface of the electrode was activated (by removing surface adsorbed contamination /processing residuals) using a base piranha solution (H2O: NH3: H2O2 in a 5:1:1 ratio) for 15-20 seconds at 80°C. Following activation, the electrode was immediately rinsed with Milli-Q water and dried under a stream of nitrogen. Then, the micropore electrode was incubated overnight in either a standard human serum albumin (HSA) solution or an aqueous cysteamine solution. The HSA layer was covalently immobilized onto the bottom gold electrode by Au-S bonds with its native exposed cysteine groups, while the initial bR layer was electrostatically coupled to the cysteamine-coated linker layer on gold. The next protein layer was bound to the first one through in situ EDC-mediated covalent coupling to form inter-protein amide bonds. Detailed protocols of the protein layer preparation were described elsewhere.