Electro-oxidation of Au(1 1 1) in contact with aqueous electrolytes: New insight from in situ vibration spectroscopy

We carried out a comprehensive study of Au(1 1 1) oxidation–reduction in the presence of (hydrogen-) sulfate ions on ideally smooth and stepped Au(S)[n(1 1 1)-(1 1 1)] single crystal electrodes using cyclic voltammetry, in situ scanning tunneling microscopy (STM) and vibration spectroscopy, such as surface-enhanced infrared absorption spectroscopy (SEIRAS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Surface structure changes and the role of surface defects in the potential regions of double layer charging and gold oxidation/reduction are discussed based on cyclic voltammetry and in situ STM data. SEIRAS and SHINERS provide complementary information on the chemical nature of adsorbates. In particular, the potential-dependent formation and stability ranges of adsorbed sulfate, hydroxide-species and of gold surface oxide could be resolved in detail. Based on our experimental observations, we proposed new and extended mechanisms of gold surface oxidation and reduction in 1.0 M H2SO4 and 1.0 M Na2SO4.

Mechanical and Chemical Stability of Injection-Molded Microcantilevers Used for Sensing

Ultraviolet-ozone treatment is used as a standard surface cleaning procedure for removal of molecular organic contamination from analytical and sensing devices. Here, it is applied for injection-molded polymer microcantilevers before characterization and sensing experiments. This article examines the effects of the surface cleaning process using commercial equipment, in particular on the performance and mechanical properties of the cantilevers. It can be shown that the first chemical aging process essentially consist of the cross linking of the polymer chains together with a physical aging of the material. For longer exposure, the expected thermo-oxidative formation of carbonyl groups sets in and an exposure dependent chemical degradation can be detected. A process time of 20 min was found suitable as a trade-off between cleaning and stability

Long Distance Electron Transfer at the Metal/Alkanethiol/Ionic Liquid Interface

The rate constants of simple electron transfer (ET) reactions in room temperature ionic liquids (ILs) available now are rather high, typically at the edge of experimental accuracy. To consider ET phenomena in these media in view of theory developed earlier for molecular solvents, it is crucial to provide quantitative comparison of experimental kinetic data for certain reactions. We report this comparison for ferrocene/ferrocenium reaction. The ET distance is fixed by Au surface modification by alkanethiol self-assembled monolayers, which were characterized by in situ scanning tunneling microscopy. The dependence of ln kapp on barrier thickness in the range of ca. 6–20 Å is linear, with a slope typical for the same plots in aqueous media. This result confirms diabatic mode of Fc oxidation at long distance. The data for shorter ET distances point to the adiabatic regime of ET at a bare gold surface, although more detailed computational studies are required to justify this conclusion.

Uptake efficiency of surface modified gold nanoparticles does not correlate with functional changes and cytokine secretion in human dendritic cells in vitro.

Engineering nanoparticles (NPs) for immune modulation require a thorough understanding of their interaction(s) with cells. Gold NPs (AuNPs) were coated with polyethylene glycol (PEG), polyvinyl alcohol (PVA) or a mixture of both with either positive or negative surface charge to investigate uptake and cell response in monocyte-derived dendritic cells (MDDCs). Inductively coupled plasma optical emission spectrometry and transmission electron microscopy were used to confirm the presence of Au inside MDDCs. Cell viability, (pro-)inflammatory responses, MDDC phenotype, activation markers, antigen uptake and processing were analyzed. Cell death was only observed for PVA-NH2 AuNPs at the highest concentration. MDDCs internalize AuNPs, however, surface modification influenced uptake. Though limited uptake was observed for PEG-COOH AuNPs, a significant tumor necrosis factor-alpha release was induced. In contrast, (PEG+PVA)-NH2 and PVA-NH2 AuNPs were internalized to a higher extent and caused interleukin-1beta secretion. None of the AuNPs caused changes in MDDC phenotype, activation or immunological properties.

Quantitative evaluation of cellular uptake and trafficking of plain and polyethylene glycol-coated gold nanoparticles

This study addresses the cellular uptake and intracellular trafficking of 15-nm gold nanoparticles (NPs), either plain (i.e., stabilized with citrate) or coated with polyethylene glycol (PEG), exposed to human alveolar epithelial cells (A549) at the air-liquid interface for 1, 4, and 24 h. Quantitative analysis by stereology on transmission electron microscopy images reveals a significant, nonrandom intracellular distribution for both NP types. No particles are observed in the nucleus, mitochondria, endoplasmic reticulum, or golgi. The cytosol is not a preferred cellular compartment for both NP types, although significantly more PEG-coated than citrate-stabilized NPs are present there. The preferred particle localizations are vesicles of different sizes (<150, 150-1000, >1000 nm). This is observed for both NP types and indicates a predominant uptake by endocytosis. Subsequent inhibition of caveolin- and clathrin-mediated endocytosis by methyl-beta-cyclodextrin (MbetaCD) results in a significant reduction of intracellular NPs. The inhibition, however, is more pronounced for PEG-coated than citrate-stabilized NPs. The latter are mostly found in larger vesicles; therefore, they are potentially taken up by macropinocytosis, which is not inhibited by MbetaCD. With prolonged exposure times, both NPs are preferentially localized in larger-sized intracellular vesicles such as lysosomes, thus indicating intracellular particle trafficking. This quantitative evaluation reveals that NP surface coatings modulate endocytotic uptake pathways and cellular NP trafficking. Other nonendocytotic entry mechanisms are found to be involved as well, as indicated by localization of a minority of PEG-coated NPs in the cytosol.

Metallic copper as an antimicrobial surface

Bacteria, yeasts, and viruses are rapidly killed on metallic copper surfaces, and the term "contact killing" has been coined for this process. While the phenomenon was already known in ancient times, it is currently receiving renewed attention. This is due to the potential use of copper as an antibacterial material in health care settings. Contact killing was observed to take place at a rate of at least 7 to 8 logs per hour, and no live microorganisms were generally recovered from copper surfaces after prolonged incubation. The antimicrobial activity of copper and copper alloys is now well established, and copper has recently been registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material. In several clinical studies, copper has been evaluated for use on touch surfaces, such as door handles, bathroom fixtures, or bed rails, in attempts to curb nosocomial infections. In connection to these new applications of copper, it is important to understand the mechanism of contact killing since it may bear on central issues, such as the possibility of the emergence and spread of resistant organisms, cleaning procedures, and questions of material and object engineering. Recent work has shed light on mechanistic aspects of contact killing. These findings will be reviewed here and juxtaposed with the toxicity mechanisms of ionic copper. The merit of copper as a hygienic material in hospitals and related settings will also be discussed.

Comparison among gold standard techniques used for the validation of methods for occlusal caries detection

The aim of this in vitro study was to assess the agreement among four techniques used as gold standard for the validation of methods for occlusal caries detection. Sixty-five human permanent molars were selected and one site in each occlusal surface was chosen as the test site. The teeth were cut and prepared according to each technique: stereomicroscopy without coloring (1), dye enhancement with rhodamine B (2) and fuchsine/acetic light green (3), and semi-quantitative microradiography (4). Digital photographs from each prepared tooth were assessed by three examiners for caries extension. Weighted kappa, as well as Friedman's test with multiple comparisons, was performed to compare all techniques and verify statistical significant differences. Results: kappa values varied from 0.62 to 0.78, the latter being found by both dye enhancement methods. Friedman's test showed statistical significant difference (P < 0.001) and multiple comparison identified these differences among all techniques, except between both dye enhancement methods (rhodamine B and fuchsine/acetic light green). Cross-tabulation showed that the stereomicroscopy overscored the lesions. Both dye enhancement methods showed a good agreement, while stereomicroscopy overscored the lesions. Furthermore, the outcome of caries diagnostic tests may be influenced by the validation method applied. Dye enhancement methods seem to be reliable as gold standard methods.

Modulation of human osteoblasts by metal surface chemistry

The use of metal implants in dental and orthopedic surgery is continuously expanding and highly successful. While today longevity and load-bearing capacity of the implants fulfill the expectations of the patients, acceleration of osseointegration would be of particular benefit to shorten the period of convalescence. To further clarify the options to accelerate the kinetics of osseointegration, within this study, the osteogenic properties of structurally identical surfaces with different metal coatings were investigated. To assess the development and function of primary human osteoblasts on metal surfaces, cell viability, differentiation, and gene expression were determined. Titanium surfaces were used as positive, and surfaces coated with gold were used as negative controls. Little differences in the cellular parameters tested for were found when the cells were grown on titanium discs sputter coated with titanium, zirconium, niobium, tantalum, gold, and chromium. Cell number, activity of cell layer-associated alkaline phosphatase (ALP), and levels of transcripts encoding COL1A1 and BGLAP did not vary significantly in dependence of the surface chemistry. Treatment of the cell cultures with 1,25(OH)2 D3 /Dex, however, significantly increased ALP activity and BGLAP messenger RNA levels. The data demonstrate that the metal layer coated onto the titanium discs exerted little modulatory effects on cell behavior. It is suggested that the microenvironment regulated by the peri-implant tissues is more effective in regulating the tissue response than is the material of the implant itself.

Influence of various surface treatments on reosseointegration around contaminated implants

The similarity of periodontitis and peri-implantitis demands for the utilization of similar principles for the treatment. Different decontamination methods were available cleaning of implant surfaces contaminated with bacteria. The aim of the present study was to evaluate the effects of various decontamination methods on reosseointegration on contaminated implants. Six mongrel dogs were used. The mandibular 1st molars and all premolars were removed bilaterally. Three months later, experi- mental implants with different surface characters were installed in each sides of the mandible. The implant consisted of two parts; the implant body and an exchangeable intraosseous implant cylinder. After osseointegration, experimental peri-implantitis was induced by cotton ligatures until the bone loss reached the junction of the two segments of the implant. After debridement of the bone defects, three treatment models were performed; (i) contaminated cylinders were removed, pristine cylinders were placed; (ii) contaminated cylinders were cleaned in situ with saline and (iii) contaminated cylinders was removed, cleaned with saline, sterilized by autoclaving. All implants were covered with membranes. After 3 months, histological evaluations were accomplished. The results indicated that in situ saline therapy demonstrated a significant difference at SLA surfaces in bone-implant-contact. Treatment of contaminated implants in situ with saline resulted in resolution of peri-implantitis and bone fill in defects.

Probing the function of ionotropic and G protein-coupled receptors in surface-confined membranes

This article reports on recent electrical and optical techniques for investigating cellular signaling reactions in artificial and native membranes immobilized on solid supports. The first part describes the formation of planar artificial lipid bilayers on gold electrodes, which reveal giga-ohm electrical resistance and the insertion and characterization of ionotropic receptors therein. These membranes are suited to record a few or even single ion channels by impedance spectroscopy. Such tethered membranes on planar arrays of microelectrodes offer mechanically robust, long-lasting measuring devices to probe the influence of different chemistries on biologically important ionotropic receptors and therefore will have a future impact to probe the function of channel proteins in basic science and in biosensor applications. In a second part, we present complementary approaches to form inside-out native membrane sheets that are immobilized on micrometer-sized beads or across submicrometer-sized holes machined in a planar support. Because the native membrane sheets are plasma membranes detached from live cells, these approaches offer a unique possibility to investigate cellular signaling processes, such as those mediated by ionotropic or G protein-coupled receptors, with original composition of lipids and proteins.

An in-situ surface electrochemistry approach toward whole-cell studies: Charge transfer between Geobacter sulfurreducens and electrified metal/electrolyte interfaces through linker molecules

Electrochemical reactivity and structure properties of electrogenic bacteria, Geobacter sulfurreducens (Gs) were studied to explore the heterogeneous electron transfer at the bacteria/electrode interface using electrochemical and in-situ spectroscopic techniques. The redox behavior of Gs adsorbed on a gold electrode, which is modified with a ω-functionalized self-assembled monolayer (SAM) of alkanethiols, depends strongly on the terminal group. The latter interacts directly with outermost cytochromes embedded into the outer membrane of the Gs cells. The redox potential of bacterial cells bound electrostatically to a carboxyl-terminated SAM is close to that observed for bacteria attached to a bare gold electrode, revealing a high electronic coupling at the cell/SAM interface. The redox potentials of bacterial cells adsorbed on amino- and pyridyl-terminated SAMs are significantly different suggesting that the outermost cytochromes changes their conformation upon adsorption on these SAMs. No redox activity of Gs was found with CH3-, N(CH3)3+- and OH-terminated SAMs. Complementary in-situ spectroscopic studies on bacteria/SAMs/Au electrode assemblies were carried out to monitor structure changes of the bacterial cells upon polarization. Spectro-electrochemical techniques revealed the electrochemical turnover of the oxidized and reduced states of outer membrane cytochromes (OMCs) in Gs, providing evidence that the OMCs are responsible for the direct electron transfer to metal electrodes, such as gold or silver, during the electricity production. Furthermore, we observed spectroscopic signatures of the native structure of the OMCs and no conformational change during the oxidation/reduction process of the microorganisms. These findings indicate that the carboxyl-anchoring group provides biocompatible conditions for the outermost cytochromes of the Gs, which facilitate the heterogeneous electron transfer at the microorganism/electrode interface.

Electrochemical characterization of self-assembled Ferrocene-terminated alkanethiol monolayers on low-index gold single crystal electrodes

We present a voltammetric and in situ STM study of 11-ferrocenyl-1-undecanethiol (FcC11) assembled on low-index single crystal and polycrystalline gold electrodes. The influence of electrode surface structure as well as of structure defects in the self-assembled FcC11 monolayers on the electrochemical response during the oxidation and reduction of the terminal ferrocene group is explored. The nature of the redox peaks is discussed in detail. We identified the coexistence of disordered FcC11 regions with 2D patches of “locally ordered” FcC11 species. We demonstrate that close-packed domains are preferentially formed at atomically flat terraces. Increasing the defect density of the substrate surface leads to a decreasing amount of locally ordered FcC11 molecules.

Adsorption interaction of carrier-free thallium species with gold and quartz surfaces

The adsorption interactions of thallium and its compounds with gold and quartz surfaces were investigated. Carrier-free amounts of thallium were produced in nuclear fusion reactions of alpha particles with thick gold targets. The method chosen for the studies was gas thermochromatography and varying the redox potential of the carrier gases. It was observed that thallium is extremely sensitive to trace amounts of oxygen and water, and can even be oxidized by the hydroxyl groups located on the quartz surface. The experiments on a quartz surface with O2, He, H2 gas in addition with water revealed the formation and deposition of only one thallium species – TlOH. The adsorption enthalpy was determined to be Δ HSiO2ads(TlOH) = −134 ± 5 kJ mol−1. A series of experiments using gold as stationary surface and different carrier gases resulted in the detection of two thallium species – metallic Tl (H2 as carrier gas) and TlOH (O2, O2+H2O and H2+H2O as pure carrier gas or carrier gas mixture) with Δ HAuads(Tl) = −270 ± 10 kJ mol− and Δ HAuads(TlOH) = −146 ± 3 kJ mol−1. These data demonstrate a weak interaction of TlOH with both quartz and gold surfaces. The data represent important information for the design of future experiments with the heavier homologue of Tl in group 13 of the periodic table – element 113 (E113).