Chemically functionalized surface patterning

Microcontact printing for patterning carbon nanotube/polymer composite films with electrical conductivity

Patterned carbon nanotube (CNT)/acrylic resin composite films were prepared using microcontact printing (μCP). To prepare ink for μCP, CNTs were dispersed into propylene glycol monomethyl ether acetate (PGMEA) solution in which acrylic resin and a commercially available dispersant (Disperbyk-2001) dissolved. The resulting ink were spin-coated onto poly(dimethylsiloxane) (PDMS) stamps. By drying solvent components from the ink, CNT/polymer composite films were prepared over PDMS stamps. Contact between the stamps and glass substrates provided CNT/polymer composite patternings on the substrates. The transfer behavior of the CNT/polymer composite films depended on the thermal-treatment temperature during μCP; thermal treatment at temperatures near the glass-transition temperature (T(g)) of the acrylic resin was effective to form uniform patternings on substrates. Moreover, contact area between polymer and substrates also affect the transfer behavior. The CNT/polymer composite films showed high electrical conductivity, despite the nonconductivity of polymer components, because CNTs in the films were interconnected. The electrical conductivity of the composite films increased as CNT content in the film became higher; as a result, the composite patternings showed almost as high electrical conductivity as previously reported CNT/polymer bulk composites.

Role of trapped air in the formation of cell-and-protein micropatterns on superhydrophobic/superhydrophilic microtemplated surfaces

Air trapped within the interstices of TiO(2) nanotube surfaces bearing superhydrophobic/superhydrophilic microtemplated domains controls formation of protein micropatterns but not cell micropatterns. Protein binding from either bovine-serum albumin (BSA) or fetal-bovine serum (FBS) solutions to superhydrophobic domains is blocked in the presence of trapped air, leading to clear protein binding contrast between superhydrophilic and superhydrophobic domains. Protein binds to superhydrophobic domains when air is displaced by sonication, leading to more protein binding to superhydrophobic domains than to superhydrophilic, with concomitantly blurred protein binding contrast. The overall contrast obtained in formation of cell (hFOB1.19, MG63, and HeLa) micropatterns depends on the cell type and protein composition of the fluid phase. All cell types preferentially attach to superhydrophilic domains from each fluid phase tested (FBS, BSA, and basal media containing no protein). All cell types do not attach to superhydrophobic domains from FBS solutions, with-or-without trapped air, creating a visually-obvious cell attachment pattern. However, cells attached to superhydrophobic domains from basal media suspensions, with-or-without trapped air, creating a blurred cell attachment pattern. Cell attachment from BSA-containing solutions gave mixed results depending on cell type. Thus, trapped air does not necessarily block cell attachment as has been suggested in the literature. Rather, cell attachment is controlled by interfacial tensions between cells, surfaces, and fluid phases in a manner that can be understood in terms of the Dupré work-of-adhesion formulation. Cell attachment patterns developed within the initial attachment phase persist for up to two days of continuous culture but overgrow thereafter, with-or-without trapped air, showing that trapped air does not block cell overgrowth over time of continuous culture.

High-throughput immunoassay through in-channel microfluidic patterning

We have developed an integrated microfluidic immunoassay chip for high-throughput sandwich immunoassay tests. The chip creates an array of reactive patterns through mechanical protection by actuating monolithically embedded button valves. We have demonstrated that this chip can achieve highly sensitive immunoassay tests within an hour, and requires only microliter samples.

Covalent layer-by-layer assembly of redox active molecular multilayers on silicon (100) by photochemical thiol-ene chemistry

The fabrication of thin organic films covalently grafted onto silicon substrates is of significant interest, as they are expected to give access to a broad range of new materials for integration into microelectronic applications. Covalent layer-by-layer (LbL) assembly offers a high degree of freedom when designing such thin films. In this work an approach for the preparation of covalent redox active molecular multilayers on silicon (100) surfaces is presented using a highly branched decaallylferrocene and thiol-ene click chemistry. The multilayers are analyzed by ellipsometry, X-ray photoelectron sprectroscopy, and cyclic voltammetry. The results indicate that the multilayer growth is linear for at least sixteen layers and the density of ferrocenes per layer is in the range of 6 × 10⁻¹¹ mol cm⁻². Moreover, this method for LbL assembly is extended to surfaces which have been locally passivated by microcontact printing. By atomic force microscopy measurements it is possible to show that the covalent LbL deposition proceeds exclusively in the nonpassivated areas.

Nanoreactors for studying single nanoparticle coarsening

The ability to observe intermediate structures as part of coarsening processes that lead to the formation of single nanoparticles (NPs) is important in gaining fundamental insight pertaining to nanostructure growth. Here, we use scanning probe block copolymer lithography (SPBCL) to create "nanoreactors" having attoliter volumes, which confine Au NP nucleation and growth to features having diameters <150 nm on a substrate. With this technique, one can use in situ TEM to directly observe and study NP coarsening and differentiate Ostwald ripening from coalescence processes. Importantly, the number of metal atoms that can engage in coarsening can be controlled with this technique, and TEM "snapshots" of particle growth can be taken. The size of the resulting nanostructures can be controlled in the 2-10 nm regime.