Capture and Release of Protein-Nanoparticle Conjugates by Reversible Covalent Molecular Linkers.

A hybrid approach to covalently detachable molecules for nanoparticle capture and release from several custom-functionalized surfaces is described. This new surface chemistry capability provides a means for reversible binding of functionalized nanoparticles without relying on costly nucleic acid-based complexation. A new surface linker motif was devised wherein custom molecules were synthesized with components for surface anchoring, cleavage, and target capture through biotin-streptavidin binding. All capture-and-release chemistry is performed using physiological conditions (aqueous, pH 7). Covalent cleavage of linker molecules was achieved through incorporation of a tunable orthogonal reversible covalent (TORC) hydrazone functional group which underwent exchange with a competitive hydrazide aided by an aniline catalyst. The influence of the linker architecture on hydrazone exchange and nanoparticle release was probed by altering the distance between hydrazone and biotin groups using different length PEG spacers. Cleavable linkers were used to functionalize microwells, magnetic separation beads, and gold-coated glass surfaces. Upon functionalization, all surface types bound streptavidin and conjugated nanoparticles regardless of the linker structure. Conversely, the extent of hydrazone exchange as well as release of nanoparticles were influenced both by the hydrazone surface density and the linker molecular structure.

Functionally decoupled soft lithography for patterning polymer brushes.

Easy soft imprint nanolithography (ESINL) is employed in the patterning of multiple olymer brushes. This new approach to soft lithography is found to be uniquely effective at patterning brushes both prior to and subsequent to grafting of the polymer chains. Silicon substrates are grafted with polystyrene, polymethylmethacrylate, and polyhydroxyethylmethacrylate using surface-initiated atom transfer radical polymerization assisted by activators generated by electron transfer (ARGET-ATRP) and characterized by contact angle measurements, infrared spectroscopy, and ellipsometry. Line grating features of 3 cm × 3 cm with critical dimensions in the range of 410-480 nm are imprinted directly over grafted brush layers or over assembled monolayers of initiator molecules and transferred to the active layer by reactive ion etching. In all cases the grating pattern is accurately reproduced in the brush layer as confirmed by atomic force microscopy, demonstrating the capability of the technique to generate large-area nanoscale patterns on a range of surface types and functionalities.

Nanoimprint lithography for functional three-dimensional patterns.

Nanoimprint lithography (NIL) is viewed as an alternative nanopatterning technique to traditional photolithography, allowing micrometer-scale and sub-hundred-nanometer resolution as well as three-dimensional structure fabrication. In this Research News article we highlight current activities towards the use of NIL in patterning active or functional materials, and the application of NIL in patterning materials that present both chemistry and structure/topography in the patterned structures, which provide scaffolds for subsequent manipulation. We discuss and give examples of the various materials and chemistries that have been used to create functional patterns and their implication in various fields as electronic and magnetic devices, optically relevant structures, biologically important surfaces, and 3D particles.

Direct passivation of hydride-terminated silicon (100) surfaces by free-radically tethered polymer brushes.

A simple and effective means for passivating crystalline silicon is reported by the use of free-radical polymerization (FRP) to directly graft polymer chains to a hydride-terminated surface (Si-H). Complete surface coverage and passivation was achieved in approximately 24 h at 60 degrees C or 30 min at 90 degrees C. Mechanistic studies determined that chain attachment followed a hydride-transfer-based grafting-to mechanism. The grafting process is compatible with a variety of monomers and was used to assemble polymer brush layers (2-12 nm thick), with grafting densities ranging from 0.02 to 0.65 chains/nm2 rivaling densities typically obtained by grafting-from scenarios. This new passivation route provides a uniquely accessible means to covalently anchor dense polymer brushes to silicon surfaces without the need for functionalization of the polymer chain ends or the substrate.

Silylcarborane acrylate nanoimprint lithography resists.

The synthesis of a novel silylcarborane acrylate monomer is reported as well as its application as an etch-resistant component for the formulation of imprint layers for UV nanoimprint lithography (NIL). By introduction of 10% by weight of the silylcarborane acrylate monomer into NIL resist formulations, the oxygen plasma etch rate of the resulting film was reduced by nearly a factor of 2. When used in NIL, the patterned resist layer had excellent oxygen plasma etch resistance, leading to effective image transfer to the underlying poly(hydroxyethyl methacrylate) lift-off layer. The latter allowed for the fabrication of metallic interdigitated electrode patterns via a NIL/lift-off process. This work demonstrates the robustness of silylcarborane-containing resists and paves the way for the investigation of new, high-resolution patterning methods.

Patterned layers of a semiconducting polymer via imprinting and microwave-assisted grafting.

Enhancements in both the rate and extent of grafting of poly(9,9'-n-dihexyl fluorene) (PDHF) onto flat and nanopatterned crosslinked photopolymer films are described. Reactivity of the surfaces toward grafting via the Yamamoto-type Ni(0)-mediated coupling reaction is increased by synthesizing and incorporating 2,7-dibromo-9-fluorenyl methacrylate (DBFM, 2) as a new grafting agent. Varying the concentration of surface-embedded DBFM is shown to control both overall graft formation and fluorescence with a maximum thickness of up to 30 nm and peak emission at 407 nm for 40 wt% loading. In addition, microwave irradiation is introduced as an effective means to drive graft formation and thus allows fabrication of PDHF-functionalized surfaces in as little as 30 min. Both forms of improvement are extended to DBFM-embedded, nanocontact-molded features ranging in size from 100 microm to 100 nm in width and 60 nm in height. Microwave-assisted grafting from these patterned surfaces produces fluorescent features as imaged by optical microscopy and a corresponding increase in feature height as measured by atomic force microscopy.

High-resolution soft lithography of thin film resists enabling nanoscopic pattern transfer.

Soft UV-imprint lithography at sub-micron dimensions was achieved in thin films of photopolymer resist. The imprinting was enabled by overcoming resist absorption by polydimethylsiloxane (PDMS) through surface treatment with a layer of (heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane. Characterization of the composite molds was done by X-ray photoelectron spectroscopy, nanoindentation, and contact angle measurements. PDMS molds treated with fluoroalkylsilane layer were used to imprint into thin films (70-630 nm) of UV curable resins consisting of either polyurethanes or acrylates, replicating with high fidelity features over the surface of wafer substrates. The use of these highly conformal PDMS molds allowed the patterning of functional materials including gold and aluminium by a simple imprint lithographic technique. This is the first report of the use of modified PDMS surfaces in an imprint process that enables the transfer of sub-micron patterns to underlying layers for device structure fabrication. The patterned features were studied with atomic force microscopy, scanning electron microscopy, and optical microscopy.

TiCp2Cl-catalyzed living radical polymerization of styrene initiated by oxirane radical ring opening.

Epoxides and paramagnetic early transition metal complexes are introduced as two new classes of initiators and catalysts, respectively, for living radical polymerizations. Thus, Ti(III)Cp2Cl synthesized in situ from the reduction of TiCp2Cl2 with Zn catalyzes the radical ring opening of oxiranes to initiate the radical polymerization of styrene. A linear dependence of molecular weight on conversion, low polydispersity, and reinitiation of the polymerization in the presence of fresh monomer indicates that the polymerization is living and that it most likely occurs by the reversible endcapping of the macroradical with Ti(III). Moreover, epoxides provide convenient access to alcohol chain ends, suitable for further transformations.