Protein function is often associated with proteins in the absorbed state at membranes or other interfaces. Surface-immobilized redox metalloproteins and metalloenzymes can also be addressed by surface-based techniques, in particular interfacial electrochemistry. The introduction of single-crystal, atomically planar metal electrode surfaces, in situ scanning tunnelling microscopy (STM) directly in aqueous buffer, and other state-of-the-art physical electrochemistry has added new perspectives to interfacial protein bioelectrochemistry. Single-crystal voltammetry enhances thus significantly voltammetric sensitivity, and in situ STM addresses single biomolecules in electron transporting action.

We overview studies in our group based on single-crystal voltammetry, interfacial capacitance, X-ray photoelectron spectroscopy, microcantilever sensor techniques, and in situ STM of several redox proteins on functionally modified Au(111)-electrode surfaces. The proteins are: Pseudomonas aeruginosa azurin (blue copper protein), Pyrococcus furiosis ferredoxin (Fe₃S₄ iron-sulfur protein), yeast cytochrome c (heme protein), and Achromobacter xylosoxidans Cu-nitrite reductase (trimeric blue copper oxidase). The data have pointed to new ways of mapping and controlling redox metalloprotein orientation and function at well-characterised electrochemical surfaces. This is important in future electrochemical biosensor design towards the single-molecule level.