Preparation and Characterization of Dendrimer Monolayers and Dendrimer−Alkanethiol Mixed Monolayers Adsorbed to Gold

Abstract

Single-component monolayers of dendrimers and two-component monolayers consisting of dendrimers and n-alkanethiols immobilized on Au substrates are described. Single-component monolayers are prepared by exposing an Au substrate to ethanolic solutions of amine- or hydroxy-terminated polyamidoamine (PAMAM) dendrimers. The resulting monolayers are highly stable and nearly close-packed for dendrimer generations ranging from 4 to 8 (G4−G8). Electrochemical ac-impedance measurements indicate that the dendrimer surface is very porous toward the electroactive redox couple Fe(CN)6 3-/4-. Ferrocene-terminated dendrimer monolayers have also been investigated. Exposure of higher-generation dendrimer monolayers to ethanolic solutions of hexadecanethiol (C16SH) results in a dramatic compression of the dendrimers, and causes them to reorient on the surface from an oblate to prolate configuration. The dendrimers originally present on the surface do not desorb as a consequence of this configurational change. Comparison of the extent of adsorption of C16SH in different media (vapor-phase N2, hexane, and ethanol) shows that solvation of the dendrimers is the primary driving force for the structural change. Finally, the reactivity and stability of the dendrimer monolayers is investigated by on-surface functionalization of the dendrimer monolayer with 4-(trifluoromethyl)benzoyl chloride. The physical and chemical properties of the single- and two-component monolayers are evaluated by using reflection infrared spectroscopy, ellipsometry, contact-angle measurements, ac-impedance spectroscopy, cyclic voltammetry, and surface acoustic wave (SAW)-based analyte-dosing experiments.

Modeling Nanosized Single Molecule Objects: Dendronized Polymers Adsorbed onto Mica

“…Indeed, computer simulations of DPs with a relatively low number of repeat units (i.e. [25][26][27][28][29][30] show end cap effects (results not shown) that resemble the deformability of dendrimers adsorbed on surfaces. In these DPs dendrons located at the two ends tend to use the available space and the hemispherical end caps to align in the direction of the macromolecular backbone, whereas in adsorbed dendrimers at low g dendrons tend to occupy the spherical free volume around the core 17 to form very flat structures.…”

Preparation of Oligonucleotide Arrays with High-Density DNA Deposition and High Hybridization Efficiency

“…24,25 The terminal groups of the immobilized dendrimers can be postfunctionalized easily without their loss from the surface. 24 A computer based simulation of the dendrimer monolayer formation has revealed that the high-generation dendrimers tend to flatten and spread on the surface, while the lowgeneration dendrimers, such as generation 1 (G1) or G2, retain their bulk-phase conformation, but are less immobilized. 23 Therefore, we assumed that G3 or G4 dendrimers retain the three-dimensional identity of dendrimers with high immobilization when forming the monolayer on the solid support.…”

“…The diameters of PAMAM G3 and G4 dendrimers are ~40 Å and ~50 Å, and the number of their terminal amine groups are 32 and 64, respectively. 24 The proposed model of molecular ordering assumes that they have highly deformed ellipsoidal shapes in condensed monolayers. 24,25 The coupling with PDC at the terminal end increases the diameter by ~17 Å.…”

“…24 The proposed model of molecular ordering assumes that they have highly deformed ellipsoidal shapes in condensed monolayers. 24,25 The coupling with PDC at the terminal end increases the diameter by ~17 Å. Therefore, the dendrimeric monolayer can provide active thiocyanate groups with the surface density of ~0.06 nmole/cm 2 .…”

Comparative analysis of response modes for gold nanoparticle biosensor based on localized surface plasmon resonance

“…We have taken refractive index for biomolecules equal to 1.46 [38,39]. Refractive index for water was estimated by the equation adopted from [40] …”