Layer-by-layer deposition of vesicles mediated by supramolecular interactions.

Vesicles are dynamic supramolecular structures with a bilayer membrane consisting of lipids or synthetic amphiphiles enclosing an aqueous compartment. Lipid vesicles have often been considered as mimics for biological cells. In this paper, we present a novel strategy for the preparation of three-dimensional multilayered structures in which vesicles containing amphiphilic ß-cyclodextrin are interconnected by proteins using cyclodextrin guests as bifunctional linker molecules. We compared two pairs of adhesion molecules for the immobilization of vesicles: mannose-concanavalin A and biotin-streptavidin. Microcontact printing and thiol-ene click chemistry were used to prepare suitable substrates for the vesicles. Successful immobilization of intact vesicles through the mannose-concanavalin A and biotin-streptavidin motifs was verified by fluorescence microscopy imaging and dynamic light scattering, while the vesicle adlayer was characterized by quartz crystal microbalance with dissipation monitoring. In the case of the biotin-streptavidin motif, up to six layers of intact vesicles could be immobilized in a layer-by-layer fashion using supramolecular interactions. The construction of vesicle multilayers guided by noncovalent vesicle-vesicle junctions can be taken as a minimal model for artificial biological tissue.

Sequence-selective detection of double-stranded DNA sequences using pyrrole-imidazole polyamide microarrays.

We describe a microarray format that can detect double-stranded DNA sequences with a high degree of sequence selectivity. Cyclooctyne-derivatized pyrrole-imidazole polyamides were immobilized on azide-modified glass substrates using microcontact printing and a strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. These polyamide-immobilized substrates selectively detected a seven-base-pair binding site incorporated within a double-stranded oligodeoxyribonucleotide sequence even in the presence of an excess of a sequence with a single-base-pair mismatch.

Modification of surfaces by chemical transfer printing using chemically patterned stamps.

The preparation of well-defined molecular monolayers and their patterning on the microscale and nanoscale are key aspects of surface science and chemical nanotechnology. In this article, we describe the modification of amine-functionalized surfaces using a new type of contact printing based on chemically patterned, flat PDMS stamps. The stamps have discrete areas with surface-bond tetrafluorophenol (TFP) groups, which allow the attachment of carboxylic acids in the presence of coupling agents such as diisopropylcarbodiimide (DIC). The generated active esters can be reacted by placing the stamps in contact with amine-functionalized surfaces. The process leads to the transfer of acyl residues from the stamp to the substrate and therefore to a covalent attachment. Patterning occurs because of the fact that reaction and transfer take place only in areas with TFP groups present on the stamp surface. Different types of amine-decorated surfaces were successfully modified, and the transfer was visualized by fluorescence microscopy. To the best of our knowledge, the covalent transfer printing (CTP) of an immobilized molecular monolayer from one surface to another surface is unprecedented.

Chemically orthogonal trifunctional Janus beads by photochemical "sandwich" microcontact printing.

The combination of topographic and chemical orthogonality on polymer particles by site selective immobilization of functional thiols via thiol-ene chemistry provides a trifunctional particle surface with azide and acid functionalities on opposing poles and alkenes in the equatorial area. These Janus beads are accessible for site selective orthogonal chemical reactions as well as biomolecular recognition on the same particle.

Immobilization of liposomes and vesicles on patterned surfaces by a peptide coiled-coil binding motif.

Patchy surfaces: An azide-terminated self-assembled monolayer was patterned with the peptide sequence (EIAALEK)(3) by using microcontact printing. This sequence forms stable coiled-coil heterodimers with the complementary peptide (KIAALKE)(3). By introducing this peptide to the surface of phospholipid liposomes and cyclodextrin vesicles, liposomes and vesicles can be immobilized at the patterned surface.

Rapid preparation of multifunctional surfaces for orthogonal ligation by microcontact chemistry.

Microcontact chemistry has been applied to patterned glass and silicon substrates by successive reaction of unprotected and monoprotected heterobifunctional linkers with alkene-terminated self-assembled monolayers (SAMs) to produce bi-, tri-, and tetrafunctional surfaces. Photochemical microcontact printing of an azide thiol linker followed by immobilization of an acid thiol linker on an undecenyl-terminated SAM results in a well-defined, micropatterned surface with terminal azide, acid, and alkene groups. Biologically relevant molecules (biotin, carbohydrates) have been selectively attached to the surface by means of orthogonal ligation chemistry, and the resulting microarrays display selective binding to fluorescently labeled proteins. An orthogonally addressable, tetrafunctional surface (azide, acid, alkene, and amine) can be prepared by an additional printing step of a tert-butyloxycarbonyl (Boc)-protected alkyne amine linker on the azide structures by using the copper(I)-catalyzed azide-alkyne Huisgen cycloaddition and subsequent removal of the protective group.

Surface patterning by microcontact chemistry.

In this Feature Article we describe recent progress in covalent surface patterning by microcontact chemistry. Microcontact chemistry is a variation of microcontact printing based on the transfer of reactive "ink" molecules from a microstructured, elastomeric stamp onto surfaces modified with complementary reactive groups, leading to a chemical reaction in the area of contact. In comparison with other lithographic methods, microcontact chemistry has a number of advantageous properties including very short patterning times, low consumption of ink molecules, high resolution and large area patterning. During the past 5 years we and many others have investigated a set of different reactions that allow the modification of flat and also spherical surfaces in an effective way. Especially click-type reactions were found to be versatile for substrate patterning by microcontact chemistry and were applied for chemical modification of reactive self-assembled monolayers and polymer surfaces. Microcontact chemistry has already found broad application for the production of functional surfaces and was also used for the preparation of DNA, RNA, and carbohydrate microarrays, for the immobilization of proteins and cells and for the development of sensors.

Photochemical microcontact printing by thiol-ene and thiol-yne click chemistry.

This article describes the microstructured immobilization of functional thiols on alkene- and alkyne-terminated self-assembled monolayers on silicon oxide substrates by photochemical microcontact printing. A photochemical thiol-ene or thiol-yne "click" reaction was locally induced in the area of contact between stamp and substrate by irradiation with UV light (365 nm). The immobilization reaction by photochemical microcontact printing was verified by contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry. The reaction rate of photochemical microcontact printing by thiol-ene chemistry was studied using time dependent contact angle measurements. The selective binding of lectins to galactoside microarrays prepared by photochemical microcontact printing was also demonstrated. It was found that photochemical microcontact printing results in a high surface coverage of functional thiols within 30 s of printing even for dilute (mM) ink solutions.

Carbohydrate microarrays by microcontact printing.

This Article describes the preparation of carbohydrate microarrays by the immobilization of carbohydrates via microcontact printing (microCP) on glass and silicon substrates. To this end, diene-modified carbohydrates (galactose, glucose, mannose, lactose, and maltose) were printed on maleimide-terminated self-assembled monolayers (SAMs). A Diels-Alder reaction occurred exclusively in the contact area between stamp and substrate and resulted in a carbohydrate pattern on the substrate. It was found that cyclopentadiene-functionalized carbohydrates could be printed within minutes at room temperature, whereas furan-functionalized carbohydrates required long printing times and high temperatures. By successive printing, microstructured arrays of up to three different carbohydrates could be produced. Immobilization and patterning of the carbohydrates on the surfaces was investigated with contact angle measurements, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and fluorescence microscopy. Furthermore, the lectins concanavalin A (ConA) and peanut agglutinin (PNA) bind to the microarrays, and the printed carbohydrates retain their characteristic selectivity toward these proteins.