1,721,250 research outputs found
Gold nanoparticles on modified glass surface as height calibration standard for atomic force microscopy operating in contact and tapping mode
No full textOptimized biorecognition of cytochrome c 551 and azurin immobilized on thiol-terminated monolayers assembled on Au(111) substrates
No full textMolecular recognition between two redox partners, azurin and cytochrome c 551, is studied at the single-molecule level by means of atomic force spectroscopy, after optimizing azurin adsorption on gold via sulfhydryl-terminated alkanethiol spacers. Our experiments provide evidence of specific interaction between the two partners, thereby demonstrating that azurin preserves biorecognition capability when assembled on gold via these spacers. Additionally, the measured single-molecule kinetic reaction rate results are consistent with a likely transient nature of the complex. Interestingly, the immobilization strategy adopted here, which was previously demonstrated to favor electrical coupling between azurin (AZ) and the metal electrode, is also found to facilitate AZ interaction with the redox partner, if compared to the case of AZ directly adsorbed on bare gold. Our findings confirm the key role of a well-designed immobilization strategy, capable of optimizing both biorecognition capabilities and electrical coupling with the conductive substrate at the single- molecule level, as a starting point for advanced applications of redox proteins for ultrasensitive biosensing
Confinement effects in pi -bonded chains at group IV semiconductor (111) surfaces
No full textThe degree of 1D character of surface chains at group IV (111)-2 × 1 reconstructed surfaces is established by surface sensitive optical spectroscopy. Optical experiments on a diamond C(111)-2 × 1 surface show that the absorption peak related to dangling-bond transitions exhibits a marked blueshift upon oxygen exposure of the clean surface. Such behaviour is analogous to that observed on a clean Si(111)-2 × 1 surface. For both surfaces the experimental finding is interpreted in terms of quantum confinement of surface electrons in quasi-one-dimensional π-bonded chains, whose length decreases with oxygen uptake. A different behaviour is observed in Ge(111)-2 × 1, where only a very slight blueshift of the surface-state optical transition is detected upon oxidation. The almost negligible blueshift in Ge(111)-2 × 1 is consistent with a significant coupling between the π-bonded chains resulting in a much less pronounced one-dimensional character of Ge(111)-2 × 1 surface electrons compared to diamond and silicon reconstructed surfaces. © 2013 IOP Publishing Ltd
Chemoprevention studies within lung cancer screening programmes
No full textWhile aggressive tobacco control and help to stop smoking are essential weapons in the fight against lung cancer, screening with low-dose computed tomography (LDCT) in high-risk populations and chemoprevention may also contribute to reducing lung cancer deaths. Persons undergoing LDCT screening are an ideal population to be tested for agents potentially able to prevent the development of lung cancer by the regression of precancerous lesions, which are routinely monitored as part of the screening process. Peripheral subsolid nodules appear as particularly suitable targets, since many are adenocarcinoma precursors. A study on inhaled budesonide (a potential chemopreventive drug) for 1 year found that the mean size of non-solid lung nodules was significantly reduced over 5 years of follow-up, compared to inhaled placebo, in a population of high-risk individuals with indeterminate lung nodules not requiring immediate specific investigation for lung cancer and detected as part of a lung cancer screening program with LDCT. A new randomised placebo-controlled phase-II trial to test the ability of aspirin to induce the regression of non-solid and partially solid nodules detected by LDCT screening has been started. The effect of aspirin on a miRNA signature able to predict the presence of both cancer and precancerous lesions in high-risk asymptomatic individuals is also being monitored in the trial. This signature was previously shown to predict the presence of both lung cancer and non-solid lung nodules in asymptomatic individuals
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Topological and electron-transfer properties of yeast cytochrome c adsorbed on bare gold electrodes
No full textThe 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
Metal/III-V Diodes Engineered by means of Si Interlayers: Interface Reactions versus Local Interface Dipoles
No full textA combined atomic force microscopy and molecular dynamics simulation study on a plastocyanin mutant chemisorbed on a gold surface
No full textA mutant of copper plastocyanin, covalently bound to an Au (111) surface through an engineered disulfide bridge, was investigated in aqueous medium by atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Tapping-mode AFM images revealed adsorption of single molecules which are homogeneously distributed over the substrate and strongly bound to gold and display uniform lateral size. A statistical analysis of the height of the macromolecules on the gold substrate evidenced a distribution around a mean value consistent with that expected from the crystallographic data and with a relatively large standard deviation. A 10-ns classical MD simulation of mutated plastocyanin, hydrated by a layer of water, covalently bound to a gold surface by one or two sulfur atoms, was performed. The simulations indicate that the bound protein retains, in both cases, its overall tertiary structure during the dynamic evolution. Moreover, the macromolecule can assume different orientations with respect to the gold substrate, which give rise to a distribution of heights on the gold substrate. Experimental and MD simulation results are compared and discussed in connection with the topological and dynamical properties of the protein system
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