Recent developments in single molecule force spectroscopy have allowed investigating the interaction between two redox partners, Azurin and Cytochrome C 551. Azurin has been directly chemisorbed on a gold electrode whereas cytochrome c has been linked to the atomic force microscopy tip by means of a heterobifunctional flexible cross-linker. When recording force-distance cycles, molecular recognition events could be observed, displaying unbinding forces of approximately 95 pN for an applied loading rate of 10 nN/s. The specificity of molecular recognition was confirmed by the significant decrease of unbinding probability observed in control block experiments performed adding free azurin solution in the fluid cell. In addition, the complex dissociation kinetics has been here investigated by monitoring the unbinding forces as a function of the loading rate: the thermal off-rate was estimated to be approximately 14 s(-1), much higher than values commonly estimated for complexes more stable than electron transfer complexes. Results here discussed represent the first studies on molecular recognition between two redox partners by atomic force microscopy.

The pivotal importance of TiO2 as a technological material involves most applications in an aqueous environment, but the single‐crystal TiO2/bulk‐water interfaces are almost completely unexplored, since up to date solid/liquid interfaces are more difficult to access than surfaces in ultrahigh vacuum (UHV). Only a few techniques (as scanning probe microscopy) offer the opportunity to explore these systems under realistic conditions. The rutile TiO2(110) surface immersed in high‐purity water is studied by in situ scanning tunneling microscopy. The large‐scale surface morphology as obtained after preparation under UHV conditions remains unchanged upon prolonged exposure to bulk water. Moreover, in contrast to UHV, atomically resolved images show a twofold periodicity along the [001] direction, indicative of an ordered structure resulting from the hydration layer. This is consistent with density‐functional theory based molecular dynamics simulations where neighboring interfacial molecules of the first water layer in contact with the bulk liquid form dimers. By contrast, this dimerization is not observed for a single adsorbed water monolayer, i.e., in the absence of bulk water.

The redox metalloprotein yeast cytochrome c was directly self-chemisorbed on "bare" gold electrodes through the free sulfur-containing group Cys102. Topological, spectroscopic, and electron transfer properties of the immobilised molecules were investigated by in situ scanning probe microscopy and cyclic voltammetry. Atomic force and scanning tunnelling microscopy revealed individual protein molecules adsorbed on the gold substrate, with no evidence of aggregates. The adsorbed proteins appear to be firmly bound to gold and display dimensions in good agreement with crystallographic data. Cyclic voltammetric analysis showed that up to 84% of the electrode surface is functionalised with electroactive proteins whose measured redox midpoint potential is in good agreement with the formal potential. Our results clearly indicate that this variant of cytochrome c is adsorbed on bare gold electrodes with preservation of morphological properties and redox functionality.

A long-standing puzzle regarding the Si(111) − 2 × 1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results.