No abstract

We demonstrate that close-packed self-assembled monolayers (SAMs) can be formed from long chain alkanethiols on the surface of electroless gold. Gold films were deposited on glass microscope slides, high-index glass, and polycarbonate “track-etch” (PCTE) membranes using an electroless plating technique. The roughness of the surface of electroless gold was large but could be reduced to levels comparable to those for evaporated films by thermal annealing of samples supported on glass substrates. Although the largest peaks in X-ray diffraction patterns corresponded to Au(111), electroless gold has significant (200), (220), and (311) reflections and is, therefore, different from Au(111) textured gold films prepared by evaporation. Self-assembled monolayers formed from alkanethiols on electroless gold were characterized by contact angles of hexadecane, cyclic voltammetry, and grazing-angle FTIR spectroscopy. To form close-packed SAMs, it was necessary to apply postplating treatments to the electroless gold such as immersion in 25% HNO3 for membrane-supported gold and thermal annealing in combination with electrochemical cleaning for glass-supported gold. The coverage of SAMs on electroless gold, as estimated from cyclic voltammograms, was greater than 99.8%. Peak positions of C−H stretching modes in IR spectra were consistent with past measurements obtained using SAMs supported on evaporated films of gold. The IR spectra suggested, however, a smaller tilt angle (from the surface normal) of the alkyl chains on electroless gold than on evaporated gold, a conclusion that is consistent with the presence of Au(200) on the surface of electroless gold.

We report here the growth and characterization of iron oxide nanoparticles by polyionic multilayers assembled by electrostatic layer-by-layer adsorption. The polyions poly(diallyldimethylammonium) chloride (PDDA) and polystyrenesulfonate (PSS) were used for the layer-by-layer assembly of the polyions. Nanoparticle nucleation was achieved by a cyclic repetition of Fe oxidative hydrolysis under an inert atmosphere. We employed UV−vis analysis for both monitoring the multilayer assembly process and ascertaining the influence of the Fe oxidative hydrolysis process on the integrity of the polymer film. No degradation of the multilayers due to the particle growth procedure was observed. The nucleation and growth of needle-shaped nanoparticles with a length of about 100 nm and a width of about 10 nm were detected by transmission electron microscopy (TEM). The void volume of the polymer matrix provided an upper limit to the particle size. As shown by selective area electron diffraction (SAED), the polycrystalline particles were identified as β-FeOOH (akaganéite), a result confirmed by reflection−absorption IR spectroscopy.

This paper reports the electroless deposition of gold onto the surface of micrometer-sized particles of silica (silica gel) and the self-assembly of monolayers formed from ω-substituted alkanethiols on the surface of the goldcoated silica gel. Whereas the proteolytic enzyme subtilisin BPN′ adsorbs irreversibly from aqueous solution (100 mM Tris buffer, 10 mM CaCl 2 , pH 8.6) onto the surface of untreated silica gel, reversible adsorption of subtilisin BPN′ is measured on silica gel coated with gold and derivatized with self-assembled monolayers (SAMs) formed from HO(CH 2 CH 2 O) 2 (CH 2 ) 11 SH. We demonstrate the usefulness of gold-coated silica gel for the preparation of stationary phases with controlled surface properties by forming a variety of mixed SAMs through coadsorption of pNA-FPAA-suc-(CH 2 ) 11 SH and X(CH 2 ) 11 SH (where X ) CH 3 , OH, or COOH). These stationary phases were used to demonstrate that the extent of enzymatic hydrolysis of pNA from the surface-immobilized tetrapeptide depends on the functional group X as well as on the dilution of the substrate within the mixed SAM. We also demonstrate that SAMs presenting biotin (X ) biotin) can be used to form multilayer structures of biomolecules on the surface of the gold-coated silica gel. These results, when combined, demonstrate the usefulness of gold-coated silica gel for the preparation of well-defined, surface-functionalized supports for biological assays.