Micro- and Nanofabrication of Robust Reactive Arrays Based on the Covalent Coupling of Dendrimers to Activated Monolayers

We report on methods to fabricate robust micro- and nanopatterned platforms, comprising high functional group densities and quasi three-dimensional structures, for possible applications in biochip array technologies. For this purpose, amine-terminated poly(amidoamine) (PAMAM) dendrimers were immobilized via amide linkage formation on 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10) self-assembled monolayers (SAMs) on gold surfaces. The coupling reaction and the resulting assemblies were characterized by grazing incidence reflection Fourier transform infrared spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy; the obtained surface coverage values were successfully fitted with a Langmuir isotherm. The fraction of unreacted peripheral primary amine groups of the surface-immobilized PAMAM dendrimers was 28% as determined by XPS analysis of trifluoroacetic anhydride-labeled assemblies. Patterning of the PAMAM dendrimers on NHS-C10 SAMs on the micrometer and sub-100-nm scale was achieved by microcontact printing and dip pen nanolithography. The resulting patterns are characterized by their high degree of order and stability of the transferred molecules due to covalent attachment

Probing Chemical Reactions at the Nanometer Scale: Inverted Chemical Force Microscopy of Reactive Self-Assembled Monolayers.

The hydrolysis and aminolysis of 11,11′-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10) adsorbed as self-assembled monolayer (SAM) on gold surfaces were monitored on the nanometer scale by a novel approach termed “inverted” chemical force microscopy (iCFM). In iCFM the reactants are immobilized on an atomic force microscopy tip rather than on the substrate and the chemical reactions that take place at the surface of the tip are probed by force–displacement measurements on an inert octadecanethiol-covered Au substrate. The information obtained is confined to the contact area at pull-off, which is of the order of only several nm2. Thus interactions and hence reaction kinetics can be quantitatively studied on the level of ~10–100 molecules. In particular, iCFM data show that the aminolysis reaction on SAMs of NHS-C10 is a spatially heterogeneous reaction. In addition information about the defect density of reactive SAMs can be obtained