SEARCH · PubMed Health

Results for “STAMPS”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75Linked to original sources

PubMed2005

Noncovalent functionalization of single-walled carbon nanotubes with water-soluble porphyrins.

We have employed water-soluble porphyrin molecules [meso-(tetrakis-4-sulfonatophenyl) porphine dihydrochloride] to solubilize single-walled carbon nanotubes (SWNTs), resulting in aqueous solutions that are stable for several weeks. The porphyrin-nanotube complexes have been characterized with absorption and fluorescence spectroscopy and with AFM. We find that the porphyrin/SWNT interaction is selective for the free base form, and that this interaction stabilizes the free base against protonation to the diacid. Under mildly acidic conditions nanotube-mediated J-aggregates form, which are unstable in solution and result in precipitation of the nanotubes over the course of a few days. Porphyrin-coated SWNTs can be precisely aligned on hydrophilic poly(dimethylsiloxane) (PDMS) surfaces by combing SWNT solution along a desired direction and then transferred to silicon substrates by stamping. Parallel SWNT patterns have been fabricated in this manner.

Letter↗

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↗

PubMed2006

Method of rapid assessment of photocatalytic activities of self-cleaning films.

An ink, comprising the redox dye resazurin (Rz) and the sacrificial electron donor glycerol, is shown to be capable of the rapid assessment of the photocatalytic activities of self-cleaning films. In the key initial stage of photocatalysis the ink changes from blue to pink. Prolonged irradiation bleaches the ink and eventually mineralizes it. The kinetics of the initial photoinduced color change is studied as a function of UV irradiance, [glycerol], [Rz], and temperature. The results reveal an apparent approximate quantum yield of 3.5 x 10(-3) and an initial rate, r(i), which increases with [glycerol] and decreases with [Rz]. It is proposed that the reduction of Rz, dispersed throughout the thick (ca. 590 nm) indicator film, may take place either via the diffusion of the dye molecules in the ink film to the surface of the underlying semiconductor layer and their subsequent reaction with photogenerated electrons and/or via the diffusion of alpha-hydroxyalkyl radicals, produced by the oxidation of the glycerol by photogenerated holes, or hydroxy radicals, away from the surface of the semiconductor into the ink film and their subsequent reaction with the dye molecules therein. The decrease in r(i) with [Rz] appears to be due to dimer formation, with the latter impeding the reduction process. The activation energy for the initial color-change process is low, ca. 9.1 +/- 0.1 kJ mol(-1) and not unlike many other photocatalytic processes. The initial rate of dye reduction appears to be directly related to the rate of destruction of stearic acid. The ink can be applied by spin-coating, stamping, or writing, using a felt-tip pen. The efficacy of such an ink for assessing the photocatalytic activity of any photocatalytic film, including those employed on commercial self-cleaning glasses, tiles, and paving stones, is discussed briefly.

Journal Article↗

PubMed2004

Thermo-biolithography: a technique for patterning nucleic acids and proteins.

We describe a "biolithographic" technique in which the unique properties of biopolymeric materials and the selective catalytic activities of enzymes are exploited for patterning surfaces under simple and bio-friendly conditions. We begin by coating a reactive film of the polysaccharide chitosan onto an inorganic surface (glass or silicon wafer). Chitosan's pH-responsive solubility facilitates film deposition, while the nucleophilic properties of this polysaccharide allow simple chemistries or biochemistries to be used to covalently attach species to the film. The thermally responsive protein gelatin is then cast on top of the chitosan film, and the gelatin gel serves as a sacrificial "thermoresist". Pattern transfer is accomplished by applying a heated stamp to melt specific regions of the gelatin thermoresist and selectively expose the underlying chitosan. Finally, molecules are conjugated to the exposed chitosan sublayer and the sacrificial gelatin layer is removed (either by treating with warm water or protease). To demonstrate the concept, we patterned a reactive dye (NHS-fluorescein), a model 20-base oligonucleotide (using standard glutaraldehyde coupling chemistries), and a model green fluorescent protein (using tyrosinase-initiated conjugation). Because gelatin can be applied and removed under mild conditions, sequential thermo-biolithographic steps can be performed without destroying previously patterned biomacromolecules. These studies represent the first step toward exploiting nature's exquisite specificity for lithographic patterning.

Biosensing Techniques↗

PubMed2004

Absorption of water by thin, ionic films of gelatin.

This paper discusses absorption of water by thin, dry films of gelatin. Experiments using a wet-stamping technique were performed to characterize water uptake in terms of (i) equilibrium profiles of the water density inside the gel and (ii) the kinetics of water absorption. It was found that, in contrast to pure gelatin films, which absorb water approximately uniformly, films of gelatin doped with ionic additives have exponentially decaying equilibrium water profiles. The process of water absorption by both doped and undoped gels was described by a theoretical model based on the minimization of grand potential functional. The results of this model are in agreement with the experiment.

Gelatin↗

PubMed2005

Patterning polymerized lipid vesicles with soft lithography.

The applications of soft lithography in patterning polymerized lipid vesicles of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine on glass substrates are reported. We demonstrate that the polymerized vesicles can be used as a high molecular weight ink to be transferred from a PDMS stamp onto a glass substrate to form two-dimensional stripes with a controlled separation. By combining channel flow with dewetting within microfluidic networks, we assemble the polymerized vesicle into three-dimensional stripes and one-dimension lines on glass substrates. Atomic force microscopy shows that these patterned vesicle structures are stable on glass substrates. The simple, stable, and precise immobilization of lipid vesicles on solid substrates will open up the possibility of integrating them in biosensors and microelectronic devices.

Journal Article↗

PubMed2004

Analysis of micro-contact printed protein patterns by SPR imaging with a LED light source.

We demonstrate the characterization of mu-contact printed protein patterns and analysis of protein-protein interactions by two-dimensional (2-D) surface plasmon resonance imaging (SPRi). Advancements in SPRi image quality from employing a light emitting diode (LED) as the light source are described. We show that a LED offers an ideal point source that can eliminate interference artifacts and speckles found when using a laser source. The attainable thickness resolution in fixed-angle imaging is comparable to that of a monochromatic source, providing a solid foundation for quantitative analysis with the system. The SPR imaging technique reported here affords sub-nanometer thickness sensitivity and micrometer lateral resolution, allowing for convenient studies of biomolecular interactions and surface morphologies of ultrathin films. Spatially well-defined protein patterns of bacterial toxins were obtained by microcontact printing using a polydimethylsiloxane (PDMS) stamp on a functionalized self-assembled monolayer on Au. The influence of protein concentration in the inking solution on transfer efficiency was investigated, and a nonlinear correlation was observed between the solution concentration and the amount of protein immobilized on the surface. Quantitative analysis of protein interaction was performed with toxin-specific antibody, showing a concentration-dependent relationship that verifies the retention of biological activity of the protein after printing. The study demonstrates the feasibility and effectiveness of using LEDs as light sources in SPR imaging, opening doors for developing compact SPR instruments for direct, sensitive, and label-free detection of biohazardous molecules.

Light↗

PubMed2005

Assembly of highly aligned DNA strands onto Si chips.

This paper reports a robust and efficient approach to assemble highly aligned DNA strands onto Si chips. The method combines advantages from molecular combing and microcontact printing to realize controlling both the density and direction of DNA strands on the Si chip. In addition, it also can be utilized to prepare stretched DNA structures on solid surfaces. Compared to approaches that use molecular combing directly on silanated surfaces, the stretched single-chain DNA structures are straighter. Furthermore, by exploiting the hydrophobic property of the intrinsic poly(dimethylsiloxane) stamp, this study also describes a simple way to produce straight bundled DNA arrays on Si and other substrates.

Adsorption↗

PubMed2006

Nonequilibrium patterns of cholesterol-rich chemical heterogenieties within single fluid supported phospholipid bilayer membranes.

We have developed a simple method to introduce cholesterol- and sphingomyelin-rich chemical heterogeneities into controlled densities and concentrations within predetermined regions of another distinct fluid phospholipid bilayer supported on a solid substrate. A contiguous primary phase--a fluid POPC bilayer displaying a well-defined array of lipid-free voids (e.g., 20-100 microm squares)--was first prepared on a clean glass surface by microcontact printing under water using a poly(dimethylsiloxane) stamp. The aqueous-phase primary bilayer pattern was subsequently incubated with secondary-phase small unilamellar vesicles composed of independent chemical compositions. Backfilling by comparable vesicles resulted in gradual mixing between the primary- and secondary-phase lipids, effacing the pattern. When the secondary vesicles consisted of phase-separating mixtures of cholesterol, sphingomyelin, and a phospholipid (2:1:1 POPC/sphingomyelin/cholesterol or 1:1:1 DOPC/sphingomyelin/cholesterol), well-defined spatial patterns of fluorescence, chemical compositions, and fluidities emerged. We conjecture that these patterns form because of the differences in the equilibration rates of the secondary liquid-ordered and liquid-disordered phases with the primary fluid POPC phase. The pattern stability depended strongly on the ambient-phase temperature, cholesterol concentration, and miscibility contrast between the two phases. When cholesterol concentration in the secondary vesicles was below 20 mol %, secondary intercalants gradually diffused within the primary POPC bilayer phase, ultimately dissolving the pattern in several minutes and presumably forming a new quasi-equilibrated lipid mixture. These phase domain micropatterns retain some properties of biological rafts including detergent resistance and phase mixing induced by selective cholesterol extraction. These patterns enable direct comparisons of cholesterol- and sphingomyelin-rich phase domains and fluid phospholipid phases for their functional preferences and may be useful for developing simple, parallelized assays for phase and chemical composition-dependent membrane functionalities.

Cholesterol↗

PubMed2006

Cross metathesis on olefin-terminated monolayers on Si(111) using the Grubbs' catalyst.

This paper reports the functionalization and patterning of olefin-terminated monolayers on Si(111) through cross metathesis. A simple, one-step synthesis of a diolefin--CH2=CH(CH2)9O(CH2)9CH=CH2--was developed from commercially available starting materials. Mixed partially olefin-terminated monolayers of this novel diolefin and 1-octadecene on hydrogen-terminated Si(111) were obtained. The olefins are raised above the rest of the monolayer and thus sterically accessible for further functionalization. Olefin-terminated monolayers were reacted with the Grubbs' first generation catalyst and olefins in solution that were terminated with fluorines, carboxylic acids, alcohols, aldehydes, and alkyl bromides. Characterization of these monolayers using X-ray photoelectron spectroscopy and horizontal attenuated total reflection infrared spectroscopy demonstrated that olefins on the surface had reacted via cross metathesis to expose fluorines, carboxylic acids, aldehydes, alcohols, and bromides. Through calibration experiments, we demonstrated a simple 1:1 correspondence between the ratio of olefins in solution used in the assembly and the final composition of the mixed monolayers. Finally, these monolayers on silicon were patterned on the micrometer-size scale by soft lithography using microfluidic channels patterned into poly(dimethylsiloxane) (PDMS) stamps. Micrometer-wide lines of polymer brushes were synthesized on these monolayers and characterized by scanning electron microscopy. In addition, olefin-terminated monolayers were patterned into micrometer-sized lines exposing carboxylic acids by cross metathesis with olefins in solution. This method of patterning is broadly applicable and can find applications in a variety of fields including the development of biosensors and nanoelectronics.

Journal Article↗

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↗

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↗

PubMed2005

Edge-spreading lithography: use of patterned photoresist structures to direct the spreading of alkanethiols on gold.

Edge-spreading lithography (ESL) has been extended to fabricate gold structures with different geometries and feature sizes on silicon substrates. In the present variant of ESL, we used photoresist structures patterned on a thin film of gold to transport alkanethiol molecules from an elastomeric stamp to the gold surface where they formed a self-assembled monolayer (SAM) along the edge of each resist feature. The emerging SAM could expand laterally on the gold via reactive spreading, during which the footprints of the resist structures were enlarged in the same fashion. Upon removal of the photoresist, selective etching of gold revealed those regions that were protected by the SAM, yielding accurate outlines of the resist features on the substrate. The width of resultant gold structures was determined by the distance over which the monolayer expanded during spreading, and could be conveniently controlled well below 200 nm by varying the contact time and/or the concentration of alkanethiol in the ink.

Journal Article↗

PubMed2005

Chemically nanopatterned surfaces using polyelectrolytes and ultraviolet-cured hard molds.

Polymer transfer printing of poly(acrylic acid) onto a polyelectrolyte multilayer platform resulted in chemically nanopatterned surfaces with well-defined structures and both positive and negative surface functionalities. A commercially available urethane-related photopolymer cured by ultraviolet light was used to make stamps for contact printing with a range of submicrometer down to 80 nm features because of its outstanding mechanical stability and inherent softening transition above 48 degrees C.

Acrylic Resins↗

PubMed2006

Laser absorption scanning tunneling microscopy of carbon nanotubes.

We report single molecule laser absorption by carbon nanotubes stamped under ultrahigh vacuum onto Si(100)2x1:H surfaces. Absorption is detected by scanning tunneling microscopy. Images are obtained with and without modulated laser excitation using lock-in amplification and a rear-illumination geometry to reduce thermal effects. Noise appears at topographic edges and is analyzed by a quantitative model in terms of scan speed, mechanical instabilities, and feedback current fluctuations at the edge of the nanotubes. Noise due to mechanical instabilities is shown to persist even in the limit of slow scan speed.

Journal Article↗

PubMed1999

Neuronal networks in vitro: formation and organization on biofunctionalized surfaces.

Receptor-mediated recognition of substrate molecules is a prerequisite for nerve cells in order to find their target structures in vivo and leads to formation of neuronal connections and networks. In order to study these mechanisms under in vitro conditions, we cultured embryonic hippocampal neurons or neuronal cell lines, SH-SY5Y and PCC7-PCC7-Mz1, onto biofunctionalized surfaces. Micropatterning on polymer surfaces, glass- and silicone-oxide-based chip materials was performed in a micrometer range by microcontact printing using polydimethylsiloxane (PDMS) stamps. Hippocampal neurons were found to form networks on chip surfaces under serum-free conditions and remained functional for more than a week. Human neuroblastoma cells SH-SY5Y as well as PCC7-Mz1 stem cells were found to follow microcontact printed pattern on polystyrene surfaces. Both cell lines showed neuronal marker expression and were cultured for up to 7 days with serum containing culture medium. Widths of 3-5 microm of coating lines were found to enhance single cell spreading along the pattern. The techniques described in this study may be useful in promoting nerve cell regeneration and organization following transection due to trauma or surgery. The neuronal alignment and network formation in vitro may furthermore serve as a model system in the field of biosensors.

Journal Article↗

PubMed2002

Prenatal and infancy home visiting by nurses: from randomized trials to community replication.

This paper summarizes a 25-year program of research that has attempted to improve the early health and development of low-income mothers and children and their future life trajectories with prenatal and infancy home visiting by nurses. The program has been tested in two separate large-scale randomized controlled trials with different populations living in different contexts. The program has been successful in improving parental care of the child as reflected in fewer injuries and ingestions that may be associated with child abuse and neglect; and maternal life-course, reflected in fewer subsequent pregnancies, greater work force participation, and reduced use of public assistance and food stamps. In the first trial, the program also produced long-term effects on the number of arrests, convictions, emergent substance use, and promiscuous sexual activity of 15-year-old children whose nurse-visited mothers were low-income and unmarried when they registered in the study during pregnancy. Since 1996, the program has been offered for public investment outside of research contexts. Careful attention has been given to ensuring that the program is replicated with fidelity to the model tested in the scientifically controlled studies by working with community leaders to ensure that organization and community contexts are favorable for the program; by providing the nurses with excellent training and technical assistance and detailed visit-by-visit guidelines; and by providing organizations with a web-based clinical information system that creates a basis for monitoring program performance and continuous quality improvement.

Child↗

PubMed2002

The coronary heart disease in-patient experience questionnaire (I-PEQ (CHD)): results from the survey of National Health Service patients.

OBJECTIVE: Analysis of data from the National Survey of Coronary Heart Disease patients to develop a core measure of patient experiences of health care. A secondary purpose was to determine whether a single summary index figure could be generated from the instrument. DESIGN: The data reported here comes from the survey of coronary heart disease (CHD) patients, which was the second in the programme of National Surveys of National Health Service (NHS) patients. It took place during 1999. After an in-patient episode for CHD, questionnaires were mailed out to patients with a covering letter and a pre-paid stamped addressed envelope. Those patients who did not reply within two weeks of the initial mailing were sent a reminder letter and, if this elicited no reply within two weeks, they were sent another copy of the questionnaire. SAMPLE: Of the 116,872 patients who were sent questionnaires, 3399 proved to be ineligible or out-of scope to the survey. Responses were gained from 84,310 (74.3% of eligible respondents). RESULTS: Reliability analysis supported the existence of seven dimensions which seem to be tapping distinct underlying phenomena: hospital environment, information and communication, patient involvement, coordination of care, discharge and transition, and pain. Higher order factor analysis indicated these dimensions constituted one factor and, consequently, can be summed to create an index figure. The construct validity of the measure was assessed, and it distinguished between groups as was hypothesised. CONCLUSIONS: The dimensions of the questionnaire have high internal reliability. Both the dimensions of the instrument and the index score were found to have high construct validity. The instrument provides a core set of issues that should be covered when assessing the quality of care for hospital patients with coronary heart disease.

Adult↗