16-mercaptohexadecanoic-acid and hydroxide-ion

Molecules of n-alkanethiols with methyl head groups typically form well-ordered monolayers during solution self-assembly for a wide range of experimental conditions. However, we have consistently observed that, for either carboxylic acid or thiol-terminated n-alkanethiols, under certain conditions nanografted patterns are generated with a thickness corresponding precisely to a double layer. To investigate the role of head groups for solution self-assembly, designed patterns of omega-functionalized n-alkanethiols were nanografted with systematic changes in concentration. Nanografting is an in situ approach for writing patterns of thiolated molecules on gold surfaces by scanning with an AFM tip under high force, accomplished in dilute solutions of desired ink molecules. As the tip is scanned across the surface of a self-assembled monolayer under force, the matrix molecules are displaced from the surface and are immediately replaced with fresh molecules from solution to generate nanopatterns. In this report, side-by-side comparison of nanografted patterns is achieved for different matrix molecules using AFM images. The chain length and head groups (i.e., carboxyl, hydroxyl, methyl, thiol) were varied for the nanopatterns and matrix monolayers. Interactions such as head-to-head dimerization affect the vertical self-assembly of omega-functionalized n-alkanethiol molecules within nanografted patterns. At certain threshold concentrations, double layers were observed to form when nanografting with head groups of carboxylic acid and dithiols, whereas single layers were generated exclusively for nanografted patterns with methyl and hydroxyl groups, regardless of changes in concentration.

Topics: Alkanes; Carboxylic Acids; Gold; Hydroxides; Microscopy, Atomic Force; Nanotechnology; Palmitic Acids; Reference Standards; Solvents; Sulfhydryl Compounds; Surface Properties; Water

Many biosensor applications are based on streptavidin (SA) binding to partially biotinylated self-assembled thiol monolayers (SAMs). In our study, binary SAMs on gold were prepared from solutions containing 16-mercapto-1-hexadecanol (thiol I) and N-(8-biotinyl-3,6-dioxa-octanamidyl)-16-mercaptohexadecanamide (thiol II) in varying component ratios. Either chloroform or ethanol was used as solvent. After 24 h thiol incubation, SA was immobilized on the resulting SAMs using the strong SA-biotin interaction. The SA binding process was monitored by QCM-D (quartz crystal microbalance monitoring dissipation factor). It is shown that the Sauerbrey equation is valid to calculate the mass quantities of the immobilized SA layers. Under the chosen incubation conditions, marginal fractions of the biotinylated component II in chloroform ((n(I)/n(II))(solution) approximately = 1000) lead to SAMs which ensure a maximal SA binding quantity of m(Sauerbrey SA) approximately = 400 ng x cm(-2), being equivalent to a SA single-layer arrangement on the SAM surface. In case of incubations from ethanolic solutions, a complete SA layer formation needs significantly higher amounts of the biotinylated component II during SAM preparation ((n(I)/n(II))(solution) approximately = 50). X-ray photoelectron spectroscopy data show that the fraction of biotinylated thiol II in the SAM determines the amount of surface-bound SA. The SAM thiol ratio ((n(I)/n(II))(SAM)) not only depends on the corresponding component ratio in the incubation solution, but is also strongly influenced by the solvent. Using chloroform as solvent during SAM preparation significantly increased the fraction of biotinylated thiol II in the SAMs compared to ethanol.

Topics: Adsorption; Biotinylation; Chloroform; Ethanol; Hydroxides; Immobilized Proteins; Palmitic Acids; Photoelectron Spectroscopy; Protein Binding; Quartz; Solvents; Streptavidin; Sulfhydryl Compounds