Results of an investigation of hydrogen-bonding mediated interparticle assembling and spatial properties from extremely dilute concentrations of the mediation agent are reported. Nanoparticles consisting of highly monodispersed decanethiolate-capped gold nanocrystal cores and R,ω-mercapto-alkanoic acids are highlighted as a model system. The formation of a stable ordered array is demonstrated via manipulating the constituents in solution. Infrared reflection spectroscopy, spectrophotometry, transmission electron microscopy, and atomic force microscopy have been utilized to probe the interparticle structural and spatial properties. A "squeezed" interparticle spatial model involving both hydrogen-bonding at the carboxylic acid groups and cohesive van der Waals interaction through interdigitation of the capping decanethiolate molecules is concluded to be responsible for the interparticle assembling forces. This interparticle spatial property depends on the relative amount of the hydrogen-bonding mediation agent, nanocrystal core size, and size monodispersity. Implications of these findings to the creation of well-defined nanostructures from nanoscale building blocks toward functional nanomaterials are also discussed.

This paper combines the topographic imaging capability of the atomic force microscope (AFM) with a compositionally patterned array of immobilized antigenic rabbit IgG on gold as an approach to performing immunoassays. The substrates are composed of micrometer-sized domains of IgG that are covalently linked to a photolithographically patterned array of a monolayer-based coupling agent. The immobilized coupling agent, which is prepared by the chemisorption of dithiobis(succinimidyl undecanoate) on gold, is separated by micrometer-sized grids of a monolayer formed from octadecanethiol (ODT). The strong hydrophobicity of the ODT adlayer, combined with the addition of the surfactant Tween 80 to the buffer solution that is used in forming the antibody-antigen pairs, minimizes the nonspecific adsorption of proteinaceous materials to the grid regions. This minimization allows the grids to function as a reference plane for the AFM detection of the height increase when a complementary antibody-antigen pair is formed. The advantageous features of this strategy, which include ease of sample preparation, an internal reference plane for the detection of topographic changes, and the potential for regeneration and reuse, are demonstrated using rabbit IgG as an immobilized antigen and goat anti-rabbit IgG as the complementary antibody. The prospects for further miniaturization are discussed.Immunoassays play a critical role in clinical, pharmaceutical, and environmental chemistries. [1][2][3] To such ends, a range of different transduction (e.g., optical, 4-6 amperometric, 7 radiochemical, 8 piezoelectric, 9-13 and capacitive 14,15 ) mechanisms have been successfully exploited for the detection of antigen-antibody binding. However, radiochemical, amperometric, and optical

The ability to prepare nanostructured metal catalysts requires the ability to control size and interparticle spatial and surface access properties. In this work, we report novel findings of an atomic force microscopic investigation of a controlled thermal activation strategy of gold catalysts nanostructured via molecular wiring or linking on a substrate surface. Gold nanocrystals of approximately 2 nm diameter capped by decanethiolate and wired by 1,9-nonanedithiolate on mica substrates were studied as a model system. By manipulating the activation temperature (200-250 degrees C), the capping/wiring molecules can be removed to produce controllable particle size and interparticle spatial morphology. The electrocatalytic activity of the activated nanostructures toward methanol oxidation, which is of fundamental importance to fuel cell catalysis, has been demonstrated. The novelty of the findings is the viability of a thermal activation strategy of core-shell nanostructured catalysts based on molecularly predefined interparticle spatial properties on a substrate, which upon further investigation may form the basis for spatially controllable nanostructured catalysts.

This paper describes the construction and characterization of miniaturized antigenic immunosurfaces composed of spontaneously adsorbed Fab′-SH fragments on gold. Rabbit Fab′-SH fragments contain a free sulfhydryl group that forms a thiolate bond with a gold substrate as detailed by X-ray photoelectron spectroscopy. This approach creates surfaces of higher epitope density, a factor critical to the early detection of disease, than surfaces composed of adsorbed whole molecule IgG on gold. The viability and specificity of antigenic Fab′-SH immunosurfaces is demonstrated using atomic force microscopy and confocal fluorescence microscopy, and possible explanations for the larger epitope density are discussed.

Dynamic contact angle studies on self-assembled thin films from C 7 F 15 CH 2 OCH 2 CH 2 CH 2 SiCl 3 reveal a range of interesting behavior. Solution-based processing conditions have been identified that allow preparation of essentially monolayer films on quartz exhibiting water adv/rec contact angles of 119/104 ( 2°and extremely low contact angle hysteresis (hexadecane adv/rec ) 74/70°, heptane adv/rec ) 56/55°) with hydrocarbon liquids. This compound provides an example of a fluorinated trichlorosilane that is able to deliver lowhysteresis films by deposition at room temperature. Adsorption of silane oligomers, formed by hydrolysis and condensation reactions in solution, was also found to occur, slower than but competitive with monolayer formation. This process became more significant as dip coating times increased. Ellipsometric data on silicon wafers confirmed that film thicknesses increased with dip time, while AFM imaging showed that the oligomeric material was deposited in the form of particulates. The effects of this process on water dynamic contact angles are discussed. We also compare contact angles on these films with those on films prepared from C n F 2n+1 CH 2 CH 2 SiCl 3 (n ) 6, 8, 10) and draw some conclusions regarding structure-property effects in these systems. Finally, we propose a mechanism that can account qualitatively for the bulk of the results observed here. Its central feature is reaction of the fluorinated alkyltrichlorosilane with surface-adsorbed water to yield a self-assembled monolayer consisting of silanetriol molecules hydrogen-bonded to the substrate. Effects of high humidity aging on dynamic contact angles of these films suggest that they are at most only lightly cross-linked when prepared under conditions utilized here.