Noncontact AFM imaging on a Si(111)2×1-Sb surface with occupied lone-pair orbitals

Force interaction between an orbital of a dangling bond out of a Si tip apex and an occupied lone-pair orbital on a Si(111)2ǵ-Sb surface is experimentally investigated to clarify the imaging mechanism of noncontact AFM. Sb adatoms with occupied lone-pair orbitals are clearly observed on the 2ǵ zigzag chain structure surface. The discontinuity in the frequency-shift curve is not observed at the Sb sites. Possible contrast mechanisms are discussed and the most understandable in terms of the chemical bonding interaction weaken by the existence of the anti-bonding orbital with one electron.     

Associative desorption of adsorbed oxygen promoted by translational energy of incident O2 molecules

Effects of the translational energy of incident oxygen molecules on surface processes from dissociative adsorption to subsequent associative desorption on Pt(1 1 1) have been investigated by means of supersonic molecular beam scattering. The reaction rate of associative desorption increases with the incident translational energy. The enhanced associative desorption can be attributed to nonthermal diffusion of dissociated oxygen, promoted by the translational energy of incoming molecules.     

Glucose oxidase-immobilized glass disks for imaging of D-glucose in acute brain slices.

A biotinylated glucose oxidase (bGOD)-immobilized glass disk was prepared for visualizing D-glucose fluxes in acute brain slices. A mouse hippocampal slice was placed on the bGOD disk and stimulated with a stimulant solution containing horseradish peroxidase (HRP) and a substrate DA-64, followed by capturing digital images of Bindschedler's Green (BG), an oxidized form of DA-64, with a CCD camera. The bGOD membranes responded proportionally to D-glucose, ranging from 2.0 to 5.0 mM. Sucrose, GABA, L-glutamic acid, L-aspartic acid, glycine, acetylcholine and L-ascorbic acid at 10 mM did not cause any responses. The D-glucose fluxes in mouse hippocampal slices stimulated by a hypoxia solution were neuronal region-dependent, i.e., dentate gyrus (DG), cornu ammonis 1 (CA1) and cornu ammonis 3 (CA3), while those stimulated by KCl was independent of the neuronal regions. The response of bGOD disks is discussed in terms of the principle, concentration dependence and selectivity.     

Potentiometric responses of polymeric liquid membranes based on hydrophobic chelating agents to metal ions.

The effect of hydrophobicity of acidic chelating agents as sensing materials on the potentiometric responses of polymeric liquid membranes was investigated. The chelating agents tested were 8-quinolinol (HOx), dithizone (HDz), 1-(2-pyridylazo)-2-naphthol (PAN) and their alkylated analogues, 5-octyloxymethyl-8-quinolinol (HO8Q), di(phexylphenyl)thiocarbazone (C6HDz), 7-pentadecyloxy-1-(2-pyridylazo)-2-naphthol (C15PAN) and a series of N-alkylcarbonyl-N-phenylhydroxylamines (CnPHA, n = 3, 6, 9, 12). The distribution coefficients between membrane solvent and water were determined to evaluate the hydrophobicity of the agents. The potential-pH profiles of the membranes containing hydrophobic chelating agents demonstrated the generation of potentiometric responses, while less hydrophobic agents gave no response. A possible model for the generation of membrane potential is proposed. The charge separation is attained by the permselective uptake of metal cations by the chelating agent anion at membrane/solution interface, where the high hydrophobicity of the agent enables the anionic or deprotonated form of the agents to remain at the membrane/solution interface.     

True atomic resolution imaging of surface structure and surface charge on the GaAs(110)

We demonstrated a novel method to detect the van der Waals and the electrostatic force interactions simultaneously on an atomic scale, which is based on frequency modulation detection method. For the first time, the surface structure and the surface charge at atomic-scale point defects on the GaAs(110) surface have been simultaneously resolved with true atomic resolution under ultra-high vacuum condition. From the bias voltage dependence of the image contrast, we can verify that the sign of the atomically resolved surface charge at the point defect was positive.     

Evaluation of concanavalin A-mannose interaction on the electrode covered with collagen film

An electrode covered with a lectin/collagen film was constructed to investigate whether the film was usable as a reaction field of binding between the lectin and sugar. The protein-sugar binding on cell surface plays an important role to various physiologic processes. The film is considered to be a cell surface, due to its biocompatibility. The immobilization of concanavalin A (Con A) which is one of proteins was attempted by an electrostatic interaction of the protonated functional groups of film to the negative charged Con A. The merit of this immobilization is that the interaction hardly causes any changes in the protein structure. Because Con A recognizes mannose moiety, the mannose was labeled with an electroactive compound. The binding was estimated from the changes of the electrode response based on the holding of electroactive moiety in the binding site of Con A to the mannose moiety. However, the electrode responses of glucose and galactose labeled with the same substance did not change. The result shows that Con A is immobilized on the film and combines with labeled mannose. Therefore, it is clear that the collagen film is suitable as the reaction field to evaluate the protein-sugar binding.