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At least 685 records · Page 38Linked to original sources
PubMed2003

Transfer-printing of highly aligned DNA nanowires.

We developed a simple method of reproducibly creating highly aligned DNA nanowires without any surface modifications or special equipment. Stretched DNA molecules initially present on the PDMS sheet were transferred onto another surface using transfer-printing (TP). Fluorescent microscopic and atomic force microscopic images revealed that many DNA molecules were highly aligned on surfaces after TP. Furthermore, it was also possible to realize the two-dimensional assembly of DNA nanowires by repeating TP.

Bacteriophage lambda↗
PubMed2006

Light stamping lithography: microcontact printing without inks.

We report a new patterning method, called light-stamping lithography (LSL), that uses UV-induced adhesion of poly(dimethylsiloxane) (PDMS). LSL is based on the direct transfer of the contact surface of the PDMS stamp to a substrate via a UV (254 nm)-induced surface bonding between the stamp and the substrate. This procedure can be adopted in automated printing machines that generate patterns with a wide range of feature sizes on diverse substrates. To demonstrate its usefulness, the LSL method was applied to prepare several PDMS patterns on a variety of substrates. The PDMS patterns were then used as templates for selective deposition of TiO2 thin film using atomic layer deposition as well as resists for selective wet etching.

Journal Article↗
PubMed2006

Patterning of robust self-assembled n-type hexaazatrinaphthylene-based nanorods and nanowires by microcontact printing.

The one-dimensional (1-D) self-assembly property of an n-type hexaazatrinaphthylene (HATNA) discotic pi-conjugated molecule was studied. Structurally robust unimolecular columnar stacks of HATNA with tunable length have been fabricated through a combination of supramolecular self-assembly and post-polymerization approach. Moreover, microcontact printing can be utilized to transfer the self-assembled nanostructures to the surface to create desired functional patterns.

Journal Article↗
PubMed2006

Order parameters and orientation distributions of solution adsorbed and microcontact printed cytochrome c protein films on glass and ITO.

The structure of solution adsorbed and microcontact printed (muCP) cytochrome c (cyt c) films on glass and indium tin oxide (ITO) was investigated using attenuated total reflectance (ATR) and total internal reflectance fluorescence (TIRF) spectroscopies to determine the orientation of the heme groups in the films. The second and fourth order parameters of the heme as well as information on the angle between the absorption and emission dipoles of the heme, gamma, were experimentally determined. The order parameters of the heme are related to the order parameters of the protein molecule using the known angle between the heme plane and the electrostatic dipole moment of the cyt c protein. The effect of the surface roughness of the substrates (glass and ITO) was also taken into account quantitatively using AFM data. Physically possible order parameters were obtained for the heme group in both solution adsorbed and muCP films, but not for the electrostatic dipole moment of the protein. In addition, the experimental values of {cos2 gamma} for immobilized zinc-substituted cyt c are greater than the values of {cos2 gamma} determined in viscous solutions, which could be an indication that the environment of the heme groups changes upon adsorption. The electron transfer behavior of solution adsorbed and muCP films on ITO, determined using electrochemical methods, is compared to their orientation distribution and surface coverage as determined by spectroscopic methods.

Adsorption↗
PubMed2003

Geometric determinants of directional cell motility revealed using microcontact printing.

Mammalian cells redirect their movement in response to changes in the physical properties of their extracellular matrix (ECM) adhesive scaffolds, including changes in available substrate area, shape, or flexibility. Yet, little is known about the cell's ability to discriminate between different types of spatial signals. Here we utilize a soft-lithography-based, microcontact printing technology in combination with automated computerized image analysis to explore the relationship between ECM geometry and directional motility. When fibroblast cells were cultured on fibronectin-coated adhesive islands with the same area (900 micrometers2) but different geometric forms (square, triangle, pentagon, hexagon, trapezoid, various parallelograms) and aspect ratios, cells preferentially extended new lamellipodia from their corners. In addition, by imposing these simple geometric constraints through ECM, cells were directed to deposit new fibronectin fibrils in these same corner regions. These data indicate that mammalian cells can sense edges within ECM patterns that exhibit a wide range of angularity and that they use these spatial cues to guide where they will deposit ECM and extend new motile processes during the process of directional migration.

Animals↗
PubMed2004

Selective atomic layer deposition of titanium oxide on patterned self-assembled monolayers formed by microcontact printing.

We demonstrate a selective atomic layer deposition of TiO2 thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the TiO2 thin film using atomic layer deposition. The selective atomic layer deposition is based on the fact that the TiO2 thin film is selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.

Journal Article↗
PubMed2004

Effect of stamp deformation on the quality of microcontact printing: theory and experiment.

Microcontact printing (microCP) is an effective way to generate micrometer- or submicrometer-sized patterns on a variety of substrates. However, the fidelity of the final pattern depends critically on the coupled phenomena of stamp deformation, fluid transfer between surfaces, and the ability of the ink to self-assemble on the substrate. In particular, stamp deformation can produce undesirable effects that limit the practice and precision of microCP. Experimental observations and comparison with theoretical predictions are presented here for three of the most undesirable consequences of stamp deformation: (1) roof collapse of low aspect ratio recesses, (2) buckling of high aspect ratio plates, and (3) lateral sticking of high aspect ratio plates. Stamp behavior was observed visually with an inverted optical microscope while load-displacement data were collected during compression and retraction of stamps. Additionally, a "robotic stamper" was used to deliver ink patterns in precise locations on substrates. These monomolecular ink patterns were then observed in high contrast using the surface potential scanning mode of an atomic force microscope. Theoretical models based on continuum mechanics were used to accurately predict both physical deformation of the stamp and the resultant inking patterns. The close agreement between these models and the experimental data presented clearly demonstrates the essential considerations one must weigh when designing stamp geometry, material, and loading conditions for optimal pattern fidelity.

Journal Article↗
PubMed2004

Spreading of 16-mercaptohexadecanoic acid in microcontact printing.

Spreading in microcontact printing refers to the process or processes by which the ink molecules end up in the parts of the substrate that are adjacent to the contacted areas but which are not contacted themselves. This has been investigated for different inking concentrations of 16-mercaptohexadecanoic acid (MHDA). Spreading of MHDA takes place with retention of a well-defined demarcation. Feature sizes can be controlled by varying the contact times. Spreading, however, only takes place beyond a certain threshold concentration. For low ink concentrations the edges of stamp features dominate the ink transfer. For these low concentrations the extent of this edge dominance depends strongly on ink concentration rather than on contact time. These observations indicate a dominant role of the stamp surface in the processes of pattern formation and spreading.

Journal Article↗
PubMed2004

Improved surface chemistries, thin film deposition techniques, and stamp designs for nanotransfer printing.

Nanotransfer printing represents an additive approach for patterning thin layers of solid materials with nanometer resolution. The surface chemistries, thin film deposition techniques, and stamp designs are all important for the proper operation of this method. This paper presents some details concerning processing procedures and other considerations needed for patterning two- and three-dimensional nanostructures with low density of defects and minimal distortions.

Journal Article↗
PubMed2004

Patterned poly(N-isopropylacrylamide) brushes on silica surfaces by microcontact printing followed by surface-initiated polymerization.

Patterned poly(N-isopropylacrylamide) (PNIPAAm) brushes were fabricated on oxidized silicon wafers by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide from a micropatterned initiator. The patterned surface initiator was prepared by microcontact-printing octadecyltrichlorosilane and backfilling with 3-(aminopropyl)triethoxysilane followed by amidization with 2-bromo-2-methylpropionic acid. XPS and FTIR confirmed the chemical structure of the surface initiator and the PNIPAAm brushes. Surface analysis techniques, including ellipsometry, contact angle goniometry, and X-ray reflectometry (XRR), were used to characterize the thickness, roughness, hydrophilicity, and density of the polymer brushes. Tapping-mode AFM imaging confirmed the successful patterning of the PNIPAAm brushes on the oxidized silicon substrates. Variable temperature ellipsometry indicated that the lower critical solution temperature of the hydrated PNIPAAm brush was broad, occurring over the range of 20-35 degrees C. A solvatochromic fluorophore, 6-propionyl-2-dimethylaminonaphthalene (Prodan), in the PNIPAAm brush layers yielded a very similar emission to that in DMF, which can be attributed to the similarity of their chemical structures. Fluorescence microscopy further proved the successful patterning of the polymer brushes and suggested that the Prodan is localized in the patterned PNIPAAm brushes and excluded from the surrounding octadecyltrichlorosilane regions.

Acrylic Resins↗
PubMed2004

Selective electroless metal deposition using microcontact printing of phosphine-phosphonic acid inks.

We report a low-cost approach to selectively deposit films of nickel and copper on glass substrates. Our approach uses microcontact printing of organic inks containing phosphonic acid groups to bind the ink to a glass substrate and phosphine groups to bind a colloidal catalyst that initiates electroless metallization. We demonstrate this procedure by fabricating patterned nickel and copper films with areas as large as 15 cm2 and minimum feature sizes of approximately 2 microm. We present studies on the use of two ink types, an oligomer and a bifunctional molecule, and demonstrate that pattern quality and adhesion of the metallized films depends on the molecular weight of the ink and the ratio of phosphine and phosphonic acid groups.

Journal Article↗
PubMed2006

Scanning force microscopy and fluorescence microscopy of microcontact printed antibodies and antibody fragments.

Unlabeled primary immunoglobulin G (IgG) antibodies and its F(ab')2 and Fc fragments were attached to oxygen-plasma-cleaned glass substrates using either microcontact printing (MCP) or physical adsorption during bath application from dilute solutions. Fluorescently labeled secondary IgGs were then bound to surface-immobilized IgG, and the relative surface coverage was determined by measuring the fluorescence intensity. Results indicated that the surface coverage of IgG increased with increasing protein solution concentration for both MCP and bath-applied IgG and that a greater concentration of IgG was transferred to a glass substrate using MCP than during physisorption during bath applications. Scanning force microscopy (SFM) showed that patterned MCP IgG monolayers were 5 nm in height, indicating that IgG molecules lie flat on the substrate. After incubation with a secondary IgG, the overall line thickness increased to around 15 nm, indicating that the secondary IgG was in a more vertical orientation with respect to the substrate. The surface roughness of these MCP patterned IgG bilayers as measured by SFM was observed to increase with increasing surface coverage. Physisorption of IgG to both unmodified patterned polydimethylsiloxane (PDMS) stamps and plasma-cleaned glass substrates was modeled by Langmuir adsorption kinetics yielding IgG binding constants of K(MCP) = 1.7(2) x 10(7) M(-1) and K(bath) = 7.8(7) x 10(5) M(-1), respectively. MCP experiments involving primary F(ab')2 and Fc fragments incubated in fluorescently labeled fragment-specific secondary IgGs were carried out to test for the function and orientation of IgG. Finally, possible origins of MCP stamping defects such as pits, pull outs, droplets, and reverse protein transfer are discussed.

Adsorption↗
PubMed2006

Three-dimensional metallized features on polymeric substrates by microcontact printing.

We demonstrate the formation of 3-D metallized features on a polymeric substrate by microcontact printing. A patterned silicon stamp was "inked" with catalytic particles. Thereafter, particles were selectively removed from the raised regions of the stamp. A molten polymer was embossed against the stamp. Upon cooling and separation, the catalytic particles that were within the recessed areas of the stamp were transferred to the polymer. The polymer was then immersed in an electroless plating bath, and metallization occurred selectively on the areas where the catalytic particles were present. We have achieved 3-D metallized columns as small as 500 nm in diameter and about 1 mum tall.

Journal Article↗
PubMed2006

Seeded-growth approach to selective metallization of microcontact-printed patterns.

We report on a versatile nanocolloidal route to obtain large-scale conducting metal microstructures on a silicon oxide substrate. By using microcontact printing of an aminosilane, we create functionalized regions on the silicon oxide surface onto which gold nanoparticles selectively adhere. By using an established electroless, seeded-growth process, the individual, isolated gold nanocrystals are enlarged past the percolation threshold to form conducting metal structures. Quantitative characterization of metal coverage, thickness, and roughness has been performed with scanning electron microscopy and spectroscopic ellipsometry.

Journal Article↗
PubMed2006

Multilayer transfer printing on microreservoir-patterned substrate employing hydrophilic composite mold for selective immobilization of biomolecules.

In this study, we introduce a hydrophilic composite mold with elasticity and moderate water permeability, suitable for transferring water-soluble polar molecules such as polyelectrolyte multilayer. This composite mold is constructed from two UV-curable polymers-Norland Optical Adhesives (NOA) 63, a urethane-related polymer, and poly(ethylene glycol) diacrylate (PEGDA). The mixture of inherently hard NOA 63 and hydrogel precursor, PEGDA, resulted in an optically transparent mold with some degree of elasticity and enhanced water permeability upon UV polymerization. Employing the NOA 63-PEGDA composite mold, a polyelectrolyte multilayer comprising alternate thin layers of poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) was transfer-printed onto arrays of microreservoir-patterned substrate to selectively prevent unwanted adsorption of biomolecules on the protruding surface. Antibody was immobilized selectively inside the microreservoirs where multilayer was not transferred, and a specific antibody binding reaction was detected inside the microreservoirs. Furthermore, the potential of this composite mold as a convenient tool for constructing a biosensor for detecting Escherichia coli (E. coli) O157:H7 was explored.

Antibodies↗
PubMed2006

Peptides on GaAs surfaces: comparison between features generated by microcontact printing and dip-pen nanolithography.

Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) were employed to understand the size, composition, and conformation of lithographic patterns composed of peptide molecules. GaAs surfaces were patterned by microcontact printing (microCP) and dip-pen nanolithography (DPN) using a peptide sequence composed of 15 amino acids. The detailed surface evaluation showed that the patterns have similar chemical compositions but differ in the bonding among the molecules anchored on the GaAs substrate. Both types of patterns were crystalline-like in nature. The features created by DPN exhibited interchain hydrogen bonding, while the ones generated by microCP displayed non-hydrogen bonding. The differences in the lithographic structures can be utilized in future biorecognition experiments that take advantage of the electronic properties of the GaAs substrate and the tunable behavior of the covalently anchored biomolecules on the surface.

Arsenicals↗
PubMed2006

Heavyweight dendritic inks for positive microcontact printing.

Poly(propylene imine) dendrimers with dialkyl sulfide end groups were prepared and developed as inks for positive microcontact printing ((+)muCP) on gold. Long (C10H21-S-C10H20-), medium (C3H7-S-C4H8-), and short (CH3-S-CH2-) dialkyl sulfide end groups were attached to second- and third-generation PPI dendrimers to create a family of dendritic sulfides. The dendritic inks flatten upon adsorption and form monolayers on gold. (+)muCP was performed on gold using commercially available poly(dimethylsiloxane) as stamp material and n-octadecanethiol as etch resist. The gold beneath the dendrimers was selectively etched away with an acidic Fe(NO3)3/thiourea solution to give the positive copy of the original master pattern. The multivalent sulfide attachment and the relatively high molecular mass of these dendrimers ensured minimal lateral ink spreading and thus optimal feature reproducibility. Contact times were varied to analyze the spreading rates of the dendritic inks. The spreading rates of the dendritic inks were found to be much lower than that of pentaerythritol tetrakis(3-mercaptopropionate). (+)muCP with the new inks was extended to submicrometer features. Optical microscopy, scanning electron microscopy, and atomic force microscopy were used to characterize the etched samples. Lines with a width of 100 nm were faithfully replicated with the third-generation dendrimers bearing medium (C3-S-C4-) end groups.

Journal Article↗
PubMed2006

Creating patterned carbon nanotube catalysts through the microcontact printing of block copolymer micellar thin films.

We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al(2)O(3)) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the PDMS features. The PDMS stamp is then put in contact with a substrate, and uniaxial compressive stress is applied to transfer the micellar thin film from the PDMS stamp onto the substrate in a defined pattern. The polymer is then removed by oxygen plasma etching to leave a patterned iron oxide nanocluster array on the substrate. Using these catalysts, we achieve patterned vertical growth of multiwalled CNTs, where the CNTs maintain the fidelity of the patterned catalyst, forming high-aspect-ratio standing structures.

Acrylates↗