Embossed polymer leaky waveguide devices for spectroscopic analysis

A combination of UV embossing, hot embossing and laminating techniques have been exploited during the fabrication of grating-coupled waveguiding devices in which the flow channel materials and geometry are designed for the effective support of light condenser modes through a sample solution. Used in conjunction with LED sources, these devices have been employed as optical platforms to obtain fluorescence emission and molecular absorption spectra in aqueous media for microTAS (micro total analytical system) applications.     

Spectroscopic techniques for the analysis of polymer surfaces and interfaces

The techniques considered are ion-scattering spectroscopy, secondary-ion mass spectrometry, x-ray photoelectron spectroscopy, internal reflection spectroscopy, diffuse reflectance spectroscopy, photoacoustic spectroscopy, other vibrational techniques, transmission spectroscopies and nuclear magnetic resonance spectroscopy. The methods are compared with respect to applicability, sensitivity, instrumentation and working conditions.     

FTIR-ATR-spectroscopic analysis of the protein adsorption on polymer blood contact surfaces

Summary Model experiments have been carried out in a flow-through attenuated total reflectance (ATR-) cell mounted in a Fourier Transform Infrared- (FTIR-) spectrometer to study in situ the adsorption of some important blood proteins on several organic and inorganic surfaces from D₂O-solutions. The model compounds used were fibrinogen, albumine and ₁-acid glycoprotein as well as polystyrene, polyetherurethane and germanium (the material of the ATR-prism).The intensities of the amide I bands of the respective adsorbed proteins were in the 10 m AU-range and have been plotted as a function of contact time between solution and surface for different reaction conditions. (Isolated, ground and negatively charged surfaces, before and after rinsing with D₂O, different pD-values.) From the data it was concluded, that the proteins adsorb in two layers, the first, irreversibly bound within a few seconds to minutes and the second build up slowly. This second layer could be removed by application of negative charge (–9 V) in the case of fibrinogen on polystyrene, and to a lesser extend for albumine and ₁-acid glycoprotein but not by rinsing with D₂O. From these IR spectra of fibrinogen, structural changes upon buildings up and desorption of the second layer as compared to the first could be derived.

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FTIR-ATR spektroskopische Analyse der Proteinadsorption an polymeren Blutkontaktoberflächen

Zusammenfassung In einem mit einer ATR-Durchflußzelle ausgestatteten Fourier-Transformations-Infrarotspektrometer wurden Modellexperimente zum In-situ-Studium der Adsorption einiger wichtiger Blutproteine an verschiedenen organischen und anorganischen Oberflächen aus D₂O-Lösung durchgeführt. Als Modellsubstanzen wurden Fibrinogen, Albumin und ₁-Glycoprotein sowie Polystyrol, Polyetherurethan und die Oberfläche des Ge-Reflexionselementes eingesetzt. Die Intensitäten der Amid-I-Banden der jeweiligen adsorbierten Proteine lagen im Bereich vonE=0,01 und wurden als Funktion der Kontaktzeit für verschiedene Reaktionsbedingungen dargestellt (isolierte, geerdete bzw. negativ geladene Oberflächen, vor und nach D₂O-Spülung, verschiedene pD-Werte). Es konnte gezeigt werden, daß die Proteine zunächst rasch eine irreversible Schicht bilden (Sekunden bis Minuten), worauf sich langsam eine zweite Schicht aufbaut. Diese konnte durch Aufladung des Reflexionselementes auf –9 V im Fall von Fibrinogen auf Polystyrol signifikant, für Albumin und ₁-Glycoprotein nur in geringerem Ausmaß wieder entfernt werden. D₂O-Spülung allein greift diese zweite Schicht nicht an. Aus den IR-Spektren dieses Fibrinogenexperiments konnten weiters Strukturänderungen während des Auf- und Abbaues der zweiten Schicht im Vergleich zur ersten abgeleitet werden.

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This work was supported by the Austrian Science Foundation (Fonds zur Förderung der wissenschaftlichen Forschung in Österreich); Proj. no. 3427.     

Fourier-transform infrared versus conventional grating-infrared-attenuated total reflectance spectroscopic investigation of the adsorption of blood proteins on polymer surfaces

Summary The advantage of Fourier-Transform-Infrared (FTIR) over conventional grating infrared spectrometry in the field of analysis of organic blood-contact surfaces has been demonstrated. It has been shown that the increase in signal-to-noise ratio by a factor of up to 100 (because of the multiplexing and throughput advantage of FTIR) and the perfect wavenumber calibration of the FTIR-system (Connes advantage) allows the study of adsorbed layers on polymer surfaces and also monitoring of the formation of protein layers on these surfaces directly from aqueous solutions. The results of clinical experiments with polyurethane and polyurethane-siloxane shunt samples are discussed.

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FTIR im Vergleich zu konventioneller Gitter-IR-ATR-spektroskopischer Untersuchung der Adsorption von Blutproteinen an Polymeroberflächen

Zusammenfassung Diese Arbeit behandelt die gegenüber der konventionellen Gitter-IR-Spektroskopie vorteilhafte Anwendung der Fourier-Transformations-Infrarot-Spektroskopie zur Analyse organischer Blutkontaktoberflächen. Das durch den Multiplex- und Strahlungsleistungsvorteil der FTIR-Methode erzielte, bis 100×höhere Signal-Rausch-Verhältnis und die genaue Wellenzahl-Eichung des FTIR-Systems (Connes-Vorteil) ermöglichen das Studium dünner Proteinschichten auf Polymeroberflächen sowie die Beobachtung der Bildung von Proteinschichten auf diesen Oberflächen direkt in wäßrigen Lösungen. Die Resultate klinischer Experimente mit Polyurethan- und Polyurethan-Siloxan-Proben werden diskutiert.

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Dedicated to Prof. Dr. H. Malissa on the occasion of his 60th birthday.

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Discussion paper presented at the 8th International Microchemical Symposium. Graz, August 25–30, 1980.

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Supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, Project no. 3427.     

Ion-induced spectroscopic methods for the analysis of surfaces,interfaces and thin films

A shift is taking place in modern surface and thin-film spectroscopic techniques from the field of surface science in a pure academic sense to problem-oriented applications related to material science and technology. This has been rendered possible and promoted among other things by a number of significant methodological and instrumental developments in ion-induced spectroscopic methods.     

Plasmochemical modification of polymer surfaces

Influence of low-temperature plasma on the polymer surface was studied with the aim of preparing polymers with required surface properties.     

Wetting of nanogrooved polymer surfaces

Molecular dynamics simulations were used to study the wetting of nanogrooved PE and PVC polymer surfaces. The contact angles, equilibrium states, and equilibrium shapes of two nanosized water droplets were analyzed on surfaces with 1D-arranged periodic roughness of various dimensions. The composite solid-liquid contact, which is preferred in practical applications and in which a droplet rests on top of the surface asperities, was observed on the roughest PE surfaces, whereas water filled the similar but slightly deeper grooves on PVC surfaces. The transition from the wetted to composite contact regime occurred when the contact angle with a flat surface reached the value at which the apparent Wenzel and Cassie contact angles are equal. Droplets on grooved PE surfaces with the composite contact exhibited contact angles in agreement with Cassie's equation, but the increase in hydrophobicity on smoother surfaces with the wetted contact was less than expected from Wenzel's equation. The difference between the simulated and theoretical values decreased as the dimensions of the surface grooves increased. Only a slight increase or even a slight decrease in the contact angles was observed on the grooved PVC surfaces, owing to the less hydrophobic nature of the flat PVC surface. On both polymers, the nanodroplet assumed a spherical shape in the composite contact. Only minor anisotropy was observed in the wetted contact on PE surfaces, whereas even a highly anisotropic shape was seen on the grooved PVC surfaces. The contact angle in the direction of the grooves was smaller than that in the perpendicular direction, and the difference between the two angles decreased with the increasing size of the water droplet.     

Plasma modification of polymer surfaces

To avoid chemical destructions of macromolecules at the polymer surface and to obtain maximum improvement in adhesion properties the short-time exposure to plasma is a good choice. Enhanced quality of surface functionalization can be reached by chemical conversion of plasma introduced functional groups. Additionally, molecular and supermolecular orientations of the macromolecules and their re-arrangement by plasma exposure influence the adhesion properties of polymers. Atmospheric pressure plasma is generally suitable for high-speed surface modification of polymers.     

NMR spectroscopic study of phosphorus-containing polymer sorbent

The nature and distribution of functional groups in the polymer matrix, as well as the nature of the spatial network in the phosphorus-containing polymeric sorbent was studied by the method of NMR spectroscopy.     

Size-dependent spectroscopic properties of conjugated polymer nanoparticles

This paper is focused on how the spectroscopic properties of conjugated polymers evolve in the size range between single polymer chains and the bulk material. The measurements used single-particle spectroscopy techniques and include both static and dynamic measurements. The main observation of this work is that the spectroscopic properties of MEH-PPV evolve rapidly as a function of nanoparticle size and achieve bulk-like properties for nanoparticles greater than 10 nm in size. Nanoparticles were assembled by a reprecipitation technique and characterized by fluorescence emission spectroscopy. The physical origin of the size-dependent spectroscopic properties is assigned to the distance dependence of four main processes: electronic energy transfer between blue and red sites, triplet-triplet annihilation, singlet exciton quenching by triplets, and singlet exciton quenching by hole polarons.     

Surface spectroscopic characterization of advanced polymer materials

The potential of a complementary use of X-ray photoelectron spectroscopy and static ToF-SIMS has been exploited with reference to the characterization of electron conducting polymers (polybithiophene) electrochemically synthetized. Particular attention has been focused on the problem of material stability under electrochemical switching.A coherent picture could be drawn showing that irreversible modifications of the surface chemistry occur, strongly dependent on the dryness of the solvent; moreover, the pathway of doping-undoping process can vary noticeably in dependence on the experimental conditions.     

Novel optical techniques for the analysis of polymer surfaces and thin films

Summary We report on novel optical techniques, based on evanescent waves, for the characterization of polymer surfaces and thin films. We first describe photo-ablation studies with polysilane films investigated by surface plasmon microscopy, a technique which is particularly well-suited for ultrathin samples. Thicker films that are homogeneous enough to carry optical waveguide modes can be characterized with high lateral resolution by the recently developed waveguide microscopy. We demonstrate this for a thin film of a solid polyelectrolyte. Finally, we report on surface plasmon field-enhanced Raman-spectroscopic and -imaging investigations of ultrathin Langmuir-Blodgett-Kuhn-layers of cadmium arachidate.W. Hickel is now with HOECHST AG, Angewandte Physik, W-6230 Frankfurt 80     

MMX polymer chains on surfaces

Fibres of [Ru(2)Br(micro-O(2)CEt)4]n polymer have been isolated on different surfaces under specific conditions, and morphologically characterised by AFM and STM, showing an unexpected helical internal structure.     

Fibronectin displacement at polymer surfaces

The interactions of fibronectin with thin polymer films are studied in displacement experiments using human serum albumin. Fibronectin adsorption and exchange on two different maleic anhydride copolymer surfaces differing in hydrophobicity and surface charge density have been analyzed by quartz crystal microbalance and laser scanning microscopy with respect to adsorbed amounts, viscoelastic properties, and conformation. Fibronectin is concluded to become attached onto hydrophilic surfaces as a "softer", less rigid protein layer, in contrast to the more rigid, densely packed layer on hydrophobic surfaces. As a result, the fibronectin conformation is more distorted on the hydrophobic substrates together with remarkably different displacement characteristics in dependence on the adsorbed fibronectin surface concentration and the displacing albumin solution concentration. While the displacement kinetic remains constant for the strongly interacting surface, an acceleration in fibronectin exchange is observed for the weakly interacting surface with increasing fibronectin coverage. For displaced amounts, no change is determined for the hydrophobic substrate, in contrast to the hydrophilic substrate with a decrease of fibronectin exchange with decreasing coverage leading finally to a constant nondisplaceable amount of adsorbed proteins. Furthermore, the variation of the albumin exchange concentration reveals a stronger dependence of the kinetic for the weakly interacting substrate with higher rates at higher albumin concentrations.     

Enhanced hydrophobicity of rough polymer surfaces

Molecular dynamics simulations were used to study the effect of periodic roughness of PE and PVC polymer surfaces on the hydrophobicity. Pillars of different lateral dimensions and heights were derived from flat crystalline surfaces, and the results of nanoscale simulations on the structured surfaces were compared with theoretical predictions of the Wenzel and Cassie equations. Hydrophobicity increased on all rough surfaces, but the increase was greater on the structured PE surfaces because of the larger water contact angle on the flat PE surface than the corresponding PVC surface. Equally sized pillar structures on the two polymers resulted in different equilibrium wetting geometries. Composite contacts were observed on rough PE surfaces, and the contact angle increased with decreasing contact area between the solid and the liquid. Opposite results were obtained for rough PVC surfaces; the contact angle increased with the solid-liquid contact area, in agreement with Wenzel's equation. However, the composite contact was observed if the energies of the wetted and composite contacts were almost equal. Good agreement was obtained between the simulated contact angles and equilibrium droplet shapes and the theories but there were also some limitations of the nanoscale simulations.     

Multitechnique characterization of fatty acid-modified microgels

The structure of fatty acid-modified hydrogel objects (microgels) created within microfluidic devices for controlled-release or sensory applications was characterized by various imaging and spectroscopic methods. Imaging with scanning electron microscopy revealed that the surface was rough and irregular on the micrometer scale. Examination of planar model systems analogous to the modified microgels with X-ray photoelectron spectroscopy and secondary ion mass spectroscopy showed that a fatty acid coating formed when the reaction conditions were conducive to covalent-bond formation. Visualization of the selectively stained lipophilic coating with laser scanning confocal microscopy while the microgel was positioned within a microfluidic channel demonstrated that the coating was confined to the microgel's periphery. Finally, using transmission electron microscopy, the thickness of the region functionalized with fatty acids was determined to be around 9 microm on samples very similar to those integrated into microfluidic devices. By using transmission electron microscopy to monitor the thickness of the fatty acid coating produced with different reaction conditions, it may be possible to customize these hybrid materials for specific sensory or controlled-release applications.     

X-ray photoelectron spectroscopic investigation of conducting polymer blends

Electrochemically prepared films of conducting polymers of polypyrrole and polythiophene and their blends with polyamide have been investigated by X-ray photoelectron spectroscopy. In the N1s region of the spectra of films containing polypyrrole the peak corresponding to N(+) at 402.0 eV is separated from that of neutral N. The intensity of the N(+) peak can be correlated with the electrical conductivity of the films and the spectroscopically derived ratio of F/N(+) is close to 4 indicating that one BF(-)(4) dopant ion is incorporated for every oxidized nitrogen center. In the spectra of films of polythiophene and its blends peaks corresponding to S and S(+) can not be resolved but again the F/C ratio correlates with the electrical conductivity.