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At least 433 records · Page 24Linked to original sources
PubMed2005

Facile synthesis of silver nanoparticles useful for fabrication of high-conductivity elements for printed electronics.

A facile synthesis of stable silver nanoparticles having a particle size of <10 nm is described. The synthesis involved reduction of silver acetate with a substituted hydrazine, such as PhNHNH2, in the presence of a 1-alkylamine, such as C16H33NH2, in toluene at 25-60 degrees C. Spin-coated thin films or printed electronic features of alkylamine-stabilized silver nanoparticles could be easily converted at 120-160 degrees C into highly conductive films or elements with conductivity of 2-4 x 104 S cm-1. Organic thin-film transistors with printed silver source/drain electrodes of this nature exhibited field-effect transistor properties which are similar to those of the devices using vacuum-deposited silver electrodes.

Journal Article↗
PubMed2005

Chemically patterned flat stamps for microcontact printing.

Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the transfer of hydrophobic n-octadecanethiol. In this case a good contrast was obtained, but the pattern was found to be susceptible to defects (cracks) in the barrier layer. Local stamp surface oxidation and subsequent modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane, for use as a barrier in the transfer of n-octadecanethiol, 16-mercaptohexadecanoic acid, and octanethiol, resulted in remarkably good contrast and stable patterns. The improved ink transfer control is ascribed to the reduction of undesired surface spreading and a superior mechanical stability of the stamp pattern. This new approach substantially expands the applicability of microcontact printing and provides a tool for the faithful reproduction of even extremely low filling ratio patterns.

Journal Article↗
PubMed2005

Single etch patterning of stacked silver and molybdenum alloy layers on glass using microcontact wave printing.

Stacked thin layers of silver alloy (AgPdCu) and MoCr layers on 10 x 15 cm2 glass substrates were patterned by microcontact wave printing and etching. Patterns of etch-resistant octadecanethiol self-assembled monolayers (SAMs) were wave printed with regular backplane stabilized PDMS stamps. Pattern development was achieved by etching both metal layers in a single step, employing a nitric acid-based etching bath. Trifluoroacetic acid and a nitrite salt were identified as essential bath components for a homogeneous etching process. Etch defects could be eliminated by the addition of a decanesulfonate, which stabilizes the SAM resist via a defect healing mechanism.

Journal Article↗
PubMed2006

Oxidized gold as an ultrathin etch resist applied in microcontact printing.

In this report it is described how a gold surface can be treated with an oxygen plasma to become an effective etch mask, with its etch resistive properties based upon electrostatic repulsion. Such a treated gold layer is only temporarily stable and may therefore be employed as a temporary etch barrier that introduces no contaminating species. Deterioration of the barrier properties can be locally expedited in a scheme that is compatible with microcontact printing. This has been achieved by the microcontact printing of a reductant on a fully oxidized gold substrate.

Journal Article↗
PubMed2006

Sum frequency generation microscopy of microcontact-printed mixed self-assembled monolayers.

Sum frequency generation imaging microscopy (SFGIM) is used to image the chemically distinct regions of a microcontact-printed monolayer surface. The contrast in the images is based on the vibrational spectrum of each component in the monolayer. Mixtures of C16 thiols on gold with CH3 and phenyl termination are imaged with a resolution of approximately 10 microm. Microcontact printing produces films that are different compared to the immersion procedure of forming self-assembled monolayers. The SFGIM technique is able to obtain a vibrational spectrum at each point on the surface and demonstrate that the stamped area has significant mixing with the molecules deposited from the backfilling solution.

Journal Article↗
PubMed2004

Molecular transfer and transport in noncovalent microcontact printing.

Microcontact printing is commonly used to create patterned films of molecules covalently bonded to substrates (e.g., thiols on gold). Here we describe microcontact printing of several types of noncovalently bonding molecules on mica. Due to the weaker interaction of the molecules with the substrate, environmental factors such as temperature and relative humidity play an important role. The vapor pressure of the inks also had a large impact on the fidelity of the stamped patterns. Fingering instabilities were observed for monolayers of octadecanol, docosanol, stearylamine, and stearic acid stamped at moderate relative humidity. The fidelity of the stamped pattern generally increased with the headgroup-surface interaction strength. These stamped monolayer films shed light on molecular transfer and two-dimensional spreading mechanisms.

Journal Article↗
PubMed2004

Imaging of affinity microcontact printed proteins by using liquid crystals.

This paper reports the design of surfaces on which thermotropic liquid crystals can be used to image affinity microcontact printed proteins. The surfaces comprise gold films deposited onto silica substrates at an oblique angle of incidence and then functionalized with a monolayer formed from 2-mercaptoethylamine. Ellipsometric measurements confirm the transfer of anti-biotin IgG to these surfaces from affinity stamps functionalized with biotinylated bovine serum albumin (BSA), while control experiments performed using anti-goat IgG confirmed the specificity of the IgG capture on the stamp. On these surfaces, anti-biotin IgG caused nematic phases of 4-cyano-4'-pentylbiphenyl (5CB, Delta epsilon = epsilon(parallel) - epsilon(perpendicular) > 0) to assume orientations that were parallel to the surfaces (planar anchoring) but with azimuthal orientations that were distinct from those assumed by the liquid crystals on the amine-terminated surfaces not supporting IgGs. Following incubation of these samples for >8 h at 36 degrees C, we observed that the amine-terminated regions of the surface not supporting IgG cause 5CB to undergo a transition from planar to perpendicular (homeotropic). Because N-(4-methoxybenzylidene)-4-butylaniline (MBBA) (Delta epsilon < 0) does not undergo a similar transition in orientation, this transition is consistent with the effects of an electrical double layer formed at the amine-terminated surface on the liquid crystal. Following the transition to homeotropic anchoring, the liquid crystals provide high optical contrast between regions of the surface supporting and not supporting IgG. We conclude that amine-terminated surfaces (I) uniformly align liquid crystals when not supporting proteins and (II) have sufficiently high surface free energy to capture proteins delivered to the surface from an affinity stamp, and thus they form the basis of a useful class of surfaces on which affinity microcontact printed proteins can be imaged using liquid crystals.

Amines↗
PubMed2006

Ink dependence of poly(dimethylsiloxane) contamination in microcontact printing.

Poly(dimethylsiloxane) (PDMS) is the most widely used stamp material in microcontact printing. It has excellent properties with respect to versatility, chemical inertness, and mechanical stability. However, it has an inclination to contaminate printed substrates with low molecular weight siloxane fragments. In this study, it is shown, by a combination of lateral force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, that the extent of the PDMS-induced contamination is dependent on the nature of the ink used. The highest degree of contamination was found for relatively polar inks, whereas apolar alkanethiol inks were found to shield the substrate from contamination. This is interpreted in terms of the contaminating species being polar in nature.

Journal Article↗
PubMed2005

Microdisplacement printing.

We describe a new patterning technique that employs microcontact printing to replace preformed labile self-assembled monolayers (SAMs) selectively; we call this "microdisplacement printing". We demonstrate that this technique results in ordered molecular regions of both the patterning ("displacing") molecule as well as the remnant labile film, here 1-adamantanethiolate. The existence of the 1-adamantanethiolate SAM before patterning hinders lateral surface diffusion of the patterning molecules, and therefore permits the use of molecules that are otherwise too mobile to pattern by other methods.

Journal Article↗
PubMed2003

Patterning axonal guidance molecules using a novel strategy for microcontact printing.

We present here a two-step strategy for micropatterning proteins on a substrate to control neurite growth in culture. First, conventional microcontact printing is used to prepare a micropattern of protein A, which binds the Fc fragment of immunoglobulins. Then, a chimeric protein, consisting of the extracellular domain of a guidance protein recombinantly linked to the Fc fragment of IgG (prepared using conventional molecular techniques), is applied from solution. The chimeric protein binds to the patterned protein A, taking on its geometric pattern. Using this method, we have micropatterned the extracellular domain of the cell adhesion molecule, L1 (as an L1-Fc chimera) and demonstrated that it retains its ability to selectively guide axonal growth. L1-Fc micropatterned on a background of poly-L-lysine resulted in selective growth of the axons on the micropattern, whereas the somata and dendrites were unresponsive. Substrates bearing simultaneous micropatterns of L1-Fc and poly-L-lysine on a background of untreated glass were also created. Using this approach, cell body position was controlled by manipulating the dimensions of the poly-L-lysine pattern, and the dendrites were constrained to the poly-L-lysine pattern, while the axons grew preferentially on L1-Fc. The two-step microcontact printing method allows preparation of substrates that contain guidance proteins in geometric patterns with resolution of approximately 1 microm. This method should be broadly applicable to many classes of proteins.

Axons↗
PubMed2000

Languages, scripts, and the environment: factors in developing concepts of print.

Preschool children bilingual in English and Hebrew were investigated for their understanding of concepts of print by means of two tasks. In the first, children had to understand that a printed word did not change its meaning if it moved to a new location. In the second, children had to make judgments about word length and ignore the size of the named objects. Previous research had shown bilingual French-English and Chinese-English children to excel in the first task, but only older Chinese-English bilinguals had an advantage in the second. The present study extended those results by investigating the effect of writing system in more detail. The study also examined the effect of the language of the environment by conducting parallel studies in environments in which either English or Hebrew was the community language. The results show that the bilingual children in both settings were more advanced than the monolinguals in both tasks and in both settings.

Child, Preschool↗
PubMed2005

Skeletal structure of printed words: evidence from the stroop task.

Do readers encode the sequencing of consonant (C) and vowel (V) phonemes (skeletal structure) in printed words? The authors used the Stroop task to examine readers' sensitivity to skeletal structure. In Experiment 1, CVC nonwords (e.g., pof) facilitated the naming of colors with congruent frames (e.g., red, a CVC word) but not with incongruent ones (e.g., green). In Experiment 2, the color black (a CCVC frame) was named faster with a congruent CCVC frame (e.g., grof) compared to either CCVCC (e.g., groft) or CVC (e.g., gof) incongruent controls. Finally, in Experiment 3, the color pink (a CVCC frame) was named faster with a CVCC frame (e.g., goft) compared to either CCVCC or CVC incongruent controls. In most cases, congruent frames shared no segments with the color name. These findings demonstrate that readers automatically assemble the skeletal structure of printed words.

Analysis of Variance↗
PubMed2001

Affinity capture of proteins from solution and their dissociation by contact printing.

Biological experiments at the solid/liquid interface, in general, require surfaces with a thin layer of purified molecules, which often represent precious material. Here, we have devised a method to extract proteins with high selectivity from crude biological sample solutions and place them on a surface in a functional, arbitrary pattern. This method, called affinity-contact printing (alphaCP), uses a structured elastomer derivatized with ligands against the target molecules. After the target molecules have been captured, they are printed from the elastomer onto a variety of surfaces. The ligand remains on the stamp for reuse. In contrast with conventional affinity chromatography, here dissociation and release of captured molecules to the substrate are achieved mechanically. We demonstrate this technique by extracting the cell adhesion molecule neuron-glia cell adhesion molecule (NgCAM) from tissue homogenates and cell culture lysates and patterning affinity-purified NgCAM on polystyrene to stimulate the attachment of neuronal cells and guide axon outgrowth.

Animals↗
PubMed1997

Flow-injection detector incorporating a screen-printed disposable amperometric biosensor for monitoring organophosphate pesticides.

The construction of a wall-jet flow cell, which houses a screen-printed amperometric pesticide biosensor, together with a complete flow-injection system, is described. This system was initially employed in studies to stabilise the enzyme acetylcholinesterase (AChE), which was immobilised on a cobalt phthalocyanine screen-printed carbon electrode to form a biosensor. A combination of dextran sulfate and lactitol, and carbodiimide for enzyme immobilisation, resulted in biosensor lifetimes of at least 76 d (at 37 degrees C). Flow-injection and biosensor conditions were optimised, then the system was evaluated by monitoring the model organophosphate pesticides (OP) dichlorvos and paraoxon. The detection limits were 7 x 10(-11) mol dm-3 (for 1 U of AChE) and 4 x 10(-11) mol dm-3 (for 0.05 U of AChE), respectively, which are better than for other electrochemical methods. Initial evaluations on two river water samples have been carried out to test the validity of the system for OP determination in field samples.

Biosensing Techniques↗
PubMed2001

Cyclodextrin-modified biosensors: comparision of cyclodextrin-linked ferrocenes as mediators in sol-gel and screen-printed formats for sensing acetylcholine.

This work reports the comparison of a sol-gel and a screen-printed biosensor format using new mediators and a sensitive thin-film (ref. 1: P. Kataky and D. Parker, Analyst, 1996, 121, 1829) to enhance the sensitivity and stability of biosensors. The new mediators were per-alkylated cyclodextrin linked ferrocenes and a control, ferrocene aminocarboxylic acid. The thin film comprised a cocktail with polyurethane, plasticiser, lipophilic anion and a perethylated beta-CD. The analyte targeted was acetylcholine using the established horseradish peroxidase-choline-oxidase-acetylcholine esterase relay. The screen-printed electrode format showed a marked decrease in oxidation potential, the magnitude of the shift depended on the structure of the mediator and the membrane covering. Although lower oxidation-potentials were observed with the sol-gel format sensors, their response was more akin to aqueous solution behaviour. Electrocatalytic currents were observed suggesting a highly efficient electron transfer process.

Journal Article↗
PubMed2003

PDMS-based microfluidic device with multi-height structures fabricated by single-step photolithography using printed circuit board as masters.

We have developed a method for fabricating microfluidic devices with multi-height structures using single step photolithography. The whole fabrication process is executed by conventional printed circuit board (PCB) technology without the need of having access to clean room facilities. Specifically designed "windows" and "rims" architectures were printed on films that were used as photomasks. Different levels of protruding features on the PCB master were produced by exposing a photomask followed by chemical wet etching. Poly(dimethylsiloxane) (PDMS) was then moulded against the positive relief master to generate microfluidic structures. In this report, we described the fabrication of a microfluidic device featured with a multi-height "sandbag" structure for particle entrapment and peripheral microchannels. Controlled immobilization of biological cells and immunocytochemcial staining assays were performed to demonstrate the applicability of the microfluidic device for cellular analysis. The integrity of the microdevice remained stable under applied pressure, indicating the robustness of the elastic PDMS structures for analytical operation. The simple microfabrication process requires only low-cost materials and minimal specialized equipment and can reproducibly produce mask lines of about 20 microm in width, which is sufficient for most microfluidic applications.

Journal Article↗
PubMed2003

Carbon nanotube screen-printed electrochemical sensors.

The fabrication, and evaluation of carbon-nanotube (CNT)-derived screen-printed (SP) electrochemical sensors based on a CNT ink are reported. The fabricated CNT strips combine the attractive advantages of CNT materials and disposable screen-printed electrodes. Such thick-film CNT sensors have a well-defined appearance, are mechanically stable, and exhibit high electrochemical reactivity.

Biosensing Techniques↗
PubMed2006

Design and fabrication of a multilayered polymer microfluidic chip with nanofluidic interconnects via adhesive contact printing.

The design and fabrication of a multilayered polymer micro-nanofluidic chip is described that consists of poly(methylmethacrylate) (PMMA) layers that contain microfluidic channels separated in the vertical direction by polycarbonate (PC) membranes that incorporate an array of nanometre diameter cylindrical pores. The materials are optically transparent to allow inspection of the fluids within the channels in the near UV and visible spectrum. The design architecture enables nanofluidic interconnections to be placed in the vertical direction between microfluidic channels. Such an architecture allows microchannel separations within the chip, as well as allowing unique operations that utilize nanocapillary interconnects: the separation of analytes based on molecular size, channel isolation, enhanced mixing, and sample concentration. Device fabrication is made possible by a transfer process of labile membranes and the development of a contact printing method for a thermally curable epoxy based adhesive. This adhesive is shown to have bond strengths that prevent leakage and delamination and channel rupture tests exceed 6 atm (0.6 MPa) under applied pressure. Channels 100 microm in width and 20 microm in depth are contact printed without the adhesive entering the microchannel. The chip is characterized in terms of resistivity measurements along the microfluidic channels, electroosmotic flow (EOF) measurements at different pH values and laser-induced-fluorescence (LIF) detection of green-fluorescent protein (GFP) plugs injected across the nanocapillary membrane and into a microfluidic channel. The results indicate that the mixed polymer micro-nanofluidic multilayer chip has electrical characteristics needed for use in microanalytical systems.

Journal Article↗