Photochemical Microcontact Printing by Tetrazole Chemistry.

We developed a simple method to pattern self-assembled monolayers of tetrazole triethoxylsilane with a variety of different molecules by photochemical microcontact printing. Under irradiation, tetrazoles form highly reactive nitrile imines, which react with alkenes, alkynes, and thiols. The covalent linkage to the surface could be unambiguously demonstrated by fluorescence microscopy, because the reaction product is fluorescent in contrast to tetrazole. The modified surfaces were further analyzed by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM), and contact angle goniometry. Protein-repellent micropatterns, a biotin-streptavidin array, and structured polymer brushes could be fabricated with this straightforward method for surface functionalization.

Supramolecular surface adhesion mediated by azobenzene polymer brushes.

Surface immobilised polymer brushes containing azobenzene units were prepared using a combination of microcontact chemistry and surface-initiated atom transfer radical polymerisation (SI-ATRP). These brushes were investigated using AFM, XPS and UV/vis spectroscopy. It was shown that two surfaces bearing azobenzene brushes can be glued together in the presence of a ß-cyclodextrin polymer and hold as much as 700 ± 150 g cm(-2).

Rewritable Polymer Brush Micropatterns Grafted by Triazolinedione Click Chemistry.

Triazolinedione (TAD) click reactions were combined with microcontact chemistry to print, erase, and reprint polymer brushes on surfaces. By patterning substrates with a TAD-tagged atom-transfer radical polymerization initiator (ATRP-TAD) and subsequent surface initiated ATRP, it was possible to graft micropatterned polymer brushes from both alkene- and indole-functionalized substrates. As a result of the dynamic nature of the Alder-ene adduct of TAD and indole at elevated temperatures, the polymer pattern could be erased while the regenerated indole substrate could be reused to print new patterns. To demonstrate the robustness of the methodology, the write-erase cycle was repeated four times.

Ultrafast Layer-by-Layer Assembly of Thin Organic Films Based on Triazolinedione Click Chemistry.

Layer-by-layer deposition is a widely used method for surface functionalization. It is shown here that up to 58 covalently linked molecular layers could be assembled in 20 min at room temperature on a silicon wafer by the layer-by-layer click reaction of a divalent triazolinedione and a trivalent diene. The layer growth was found to be linear. The multilayers were analyzed by ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy.

Surface patterning with natural and synthetic polymers via an inverse electron demand Diels-Alder reaction employing microcontact chemistry.

Bioorthogonal ligation methods are the focus of current research due to their versatile applications in biotechnology and materials science for post-functionalization and immobilization of biomolecules. Recently, inverse electron demand Diels-Alder (iEDDA) reactions employing 1,2,4,5-tetrazines as electron deficient dienes emerged as powerful tools in this field. We adapted iEDDA in microcontact chemistry (µCC) in order to create enhanced surface functions. µCC is a straightforward soft-lithography technique which enables fast and large area patterning with high pattern resolutions. In this work, tetrazine functionalized surfaces were reacted with carbohydrates conjugated with norbornene or cyclooctyne acting as strained electron rich dienophiles employing µCC. It was possible to create monofunctional as well as bifunctional substrates which were specifically addressable by proteins. Furthermore we structured glass supported alkene terminated self-assembled monolayers with a tetrazine conjugated atom transfer radical polymerization (ATRP) initiator enabling surface grafted polymerizations of poly(methylacrylate) brushes. The success of the surface initiated iEDDA via µCC as well as the functionalization with natural and synthetic polymers was verified via fluorescence and optical microscopy, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).

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.

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.

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.