where he has worked since 1993. He received his Ph.D. in Solid State Physics in 1982 and his D.Sc. in Theoretical Physics in 1998. His research covers solid state physics, the physics of liquids, theory of adsorption, many-particle physics and the theory of electrochemical electron transfer. His present research is focused on the theory of electron tunneling in bridged electrochemical contacts. He is the author or co-author of more than 60 publications in scientific journals. Qijin Chi received his Ph.D. degree in analytical and physical chemistry in 1994 from the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. After having spent one year as a DFG postdoctoral fellow at Tübingen University, Germany, and two years as a JSPS postdoctoral fellow in Tokyo, Japan, he joined the Department of Chemistry at Technical University of Denmark in 1998. He is currently a lektor (associate professor) in chemistry. Qijin Chi also studied molecular biology and biochemistry (2000-2003) at the Johns Hopkins University School of Medicine. His research interests include biological nanomaterials, electrochemistry, surface self-assembled chemistry, and biophysics. He has authored four patents, over fifty research articles, and several book chapters. Tim Albrecht graduated in chemistry at the University of Essen in 2000. He received a Ph.D. with Prof. P. Hildebrandt at the Max-Planck Institute for Radiation Chemistry (now Bioinorganic Chemistry) in Muelheim/ Germany for studies on interfacial charge transfer processes of heme proteins using spectroelectrochemistry (SE(R)RS) and electrochemical STM. He held a Marie-Curie fellowship 2004-2006 whilst working in Prof. J. Ulstrup's group and became a lecturer in Physical Chemistry at Imperial College London in 2006. His research interests include (bio)electrochemistry, charge transport through individual molecules, and electrode/nanopore architectures in single-biomolecule sensing. He has published 14 research articles, 2 book chapters, and filed 2 patent applications. Palle Skovhus Jensen obtained his M.Sc. degree in 2006 at Technical University of Denmark and is presently a Ph.D. student in Prof. J. Ulstrup's group. His research includes interfacial electrochemistry, electrochemical STM and AFM of redox metalloproteins, extending to catalysis of bioelectrochemical processes by molecular scale metallic nanoparticles. He is the co-author of several research articles in these areas.

We have shown that Pseudomonas aeruginosa azurin can be immobilized on alkanethiol monolayers self-assembled on Au(111). Immobilization is achieved through hydrophobic interactions between the hydrophobic area around the copper atom in azurin and methyl heads of alkanethiol to form submonolayers or monolayers. In this orientation mode azurin molecules on Au(111) are oriented with the redox center (copper atom) facing the electrode surface. This is opposite to the orientation of azurin on bare gold which is via a surface disulfide group such as recently reported. Scanning tunneling microscopy (STM) with molecular resolution reveals that both well-ordered alkanethiol and protein adlayers are present. Adsorbed azurin molecules exhibit high stability and retain electron transfer (ET) function. Long-range interfacial ET between azurin and Au(111) across variable-length alkanethiol bridges was systematically investigated by different electrochemical techniques. Distance-dependent ET can be controlled by adjusting the length of the alkanethiol chain. The electrochemical ET rate constant is almost independent of the chain length up to ca. 9 methylene units but follows exponential distance decay with a decay factor (β) of 1.03 ± 0.02 per CH2 unit at longer chain lengths. Overvoltage-dependent ET was also examined. The results provide a strategy to ordered molecular assemblies, and controlled orientation and ET of azurin at atomically planar metallic surfaces. This approach can in principle be extended to other redox metalloproteins.

We provide a comprehensive approach to the formation and characterization of molecular monolayers of the blue copper protein Pseudomonas aeruginosa azurin on Au(111) in aqueous ammonium acetate solution. Main issues are adsorption patterns, reductive desorption, properties of the double layer, and long-range electrochemical electron transfer between the electrode and the copper center. Voltammetry, electrochemical impedance spectroscopy (EIS), in situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) have been employed to disclose features of these issues. Zn-substituted azurin, cystine, and 1-butanethiol are investigated for comparison. Cyclic voltammetric and capacitance measurements show qualitatiVely that azurin is adsorbed at submicromolar concentrations over a broad potential range. The characteristics of reductive desorption suggest that azurin is adsorbed via its disulfide group to form a monolayer. The adsorption of this protein on Au(111) via a gold-sulfur binding mode is further supported by XPS measurements. In situ STM images with molecular resolution have been recorded and show a dense monolayer organization of adsorbed azurin molecules. Direct electron transfer (ET) between the copper atom of adsorbed azurin and the electrode has been revealed by differential pulse voltammetry. The rate constant is estimated from electrochemical impedance spectroscopy and shows that ET is compatible with a long-range ET mode such as that anticipated by theoretical frames. The results constitute the first case of an electrochemically functional redox protein monolayer at single-crystal metal electrodes.

Microscopic structures for molecular monolayers of L-cysteine and L-cystine assembled on Au(111) have been disclosed by employing electrochemistry and in situ scanning tunneling microscopy (STM). Highresolution STM images show that the adlayers of both cyteine and cystine exhibit highly-ordered networklike clusters with (3 3 × 6)R30°structure. By combining the surface coverage estimated from voltammetric data, each cluster is demonstrated to include six individual cysteine molecules or three cystine molecules. As a comparison, no cluster structure is observed for the 1-butanethiol adlayer prepared and examined under the same conditions as those for cysteine and cystine. This suggests that intermolecular and intramolecular hydrogen bonds among adsorbed cysteine or cystine molecules could be responsible for the origin of the cluster-network structures for the adlayers. Several models are proposed and used to explain the in situ STM observations in detail.

Monolayers of molecules, which retain their function in the adsorbed state on solid surfaces, are important in materials science, analytical detection, and other technology approaching the nanoscale. Molecular monolayers, including layers of functional biological macromolecules, offer new insight in electronic properties and stochastic single-molecule features and can be probed by new methods which approach the single-molecule level. One of these is in situ scanning tunneling microscopy (STM) in which single-molecule electronic properties directly in aqueous solution are probed. In situ STM combined with physical electrochemistry, single-crystal electrodes, and spectroscopic methods is now a new dimension in interfacial bioelectrochemistry. We overview first some approaches to spectroscopic single-molecule imaging, including fluorescence spectroscopy, chemical reaction dynamics, atomic force microscopy, and electrochemical single-electron transfer. We then focus on in situ STM. In addition to high structural resolution, in situ STM offers a single-molecule spectroscopic perspective. This emerges most clearly when adsorbate molecules contain accessible redox levels, and the tunneling current decomposes into successive single-molecule interfacial electron transfer (ET) steps. Theories of electrochemical ET and in situ STM of redox molecules as well as specific cases are addressed. Two-step in situ STM represents different molecular mechanisms and even new ET phenomena, related to coherent many-electron transfer. A number of systems are noted to accord with these views. The discussion is concluded by attention to one of the still very few redox proteins addressed by in situ STM, the blue copper protein Pseudomonas aeruginosa azurin. Use of comprehensive electrochemical techniques has ascertained that well-defined protein monolayers in two opposite orientations can be formed and interfacial tunneling patterns disclosed. P. aeruginosa azurin emerges as by far the most convincing case where in situ STM of functional metalloproteins to single-molecule resolution has been achieved. This comprehensive approach holds promise for broader use of in situ STM as a single-molecule spectroscopy of metalloproteins and illuminates prerequisites and limitations of in situ STM of biological macromolecules.

Electrocatalytic properties of biomimetic supported incomplete cubane-type [Mo 3 S 4 ] 4+ clusters are investigated. The activity toward the hydrogen evolution reaction (HER) is evaluated on both a high surface area gas diffusion electrode in a membrane electrode assembly and on highly orientated pyrolytic graphite (HOPG) supports. Sub-monolayers of the clusters were imaged by means of scanning tunnelling microscopy (STM) prior to electrochemical characterization. This enabled the quantification of the activity on a per cluster basis for the HER and the comparison of the activity with other HER catalysts. We find that the HER activity of the [Mo 3 S 4 ] 4+ is comparable with that of the edge sites of MoS 2 . The supported [Mo 3 S 4 ] 4+ molecules were also characterized by X-ray photoelectron spectroscopy (XPS), and the observed deterioration in electrocatalytic activity with time was assigned to slow [Mo 3 S 4 ] 4+ cathodic desorption from the catalyst support.

Bacteria form surface attached biofilm communities as one of the most important survival strategies in nature. Biofilms consist of water, bacterial cells and a wide range of self-generated extracellular polymeric substances (EPS). Biofilm formation is a dynamic self-assembly process and several distinguishable stages are observed during bacterial biofilm development. Biofilm formation is shown to be coordinated by EPS production, cell migration, subpopulation differentiation and interactions. However, the ways these different factors affect each other and contribute to community structural differentiation remain largely unknown. The distinct roles of different EPS have been addressed in the present report. Both Pel and Psl polysaccharides are required for type IV pilus-independent microcolony formation in the initial stages of biofilm formation by Pseudomonas aeruginosa PAO1. Both Pel and Psl polysaccharides are also essential for subpopulation interactions and macrocolony formation in the later stages of P. aeruginosa PAO1 biofilm formation. Pel and Psl polysaccharides have different impacts on Pseudomonas quinolone signal-mediated extracellular DNA release in P. aeruginosa PAO1 biofilms. Psl polysaccharide is more important than Pel polysaccharide in P. aeruginosa PAO1 biofilm formation and antibiotic resistance. Our study thus suggests that different EPS materials play distinct roles during bacterial biofilm formation.

Extracellular polymeric substances play important roles in microbial extracellular electron transfer processes.