Showing papers by "Franz R. Aussenegg published in 1995"

The metal island coated swelling polymer over mirror system (MICSPOMS): a new principle for measuring ionic strength

Abstract: We propose a new optical sensor principle for cases where the sensor/analyte reaction results in the change of non-spectroscopic parameters and demonstrate this for the ionic strength-dependent swelling of special polymers. The sensor material is part of an optical thin-film system which transforms the variation in volume into spectral information. The metal island coated swelling polymer over mirror system (MICSPOMS) is a special kind of optical reflection interference filter, consisting of a metal mirror, followed by a thin layer of an optical transparent interlayer, represented by the ionic strength sensitive polymer. Therefore, by monitoring the slope of the narrow bandwidth reflection minimum of this layer system a high sensitivity for the analyte, which causes the swelling, is obtained. To obtain swellability and attachment to the metal surface as well as photostructuring properties a crosslinked polyvinylpyrrolidone photopolymer was developed.

Optochemical sensor and method for production

Abstract: An optochemical sensor for measuring concentrations of analytes is provided with a reactive matrix preferably made of polymeric material capable of swelling. Further provided are a mirror layer and a layer of a plurality of discrete islands that are electrically conductive, between which layers the reactive matrix is positioned, the diameter of the islands being smaller than the wavelength of the light employed for monitoring and evaluation.

The use of metal-island-coated pH-sensitive swelling polymers for biosensor applications

Abstract: A new optical sensor principle for the case where the sensor/analyte reaction results in the change of non-spectroscopic parameters is presented. Changing the analyte concentration results in the pH-dependent swelling of special polymers. The sensor material is part of an optical thin-film system, which transforms the variations in volume of the polymer into spectral information. A crosslinked polyvinylpyrrolidone photopolymer has been developed to obtain a gel matrix showing ion/pH-dependent swelling and good attachment to the sensor surface as well as photostructuring properties. For the construction of a biosensor, the device is covered by a photostructured polyvinylpyrrolidone membrane incorporating the desired enzymes. Urea is quantified by using immobilised urease that converts the analyte into carbon dioxide and ammonia.

Investigation of localized surface plasmons with the photon scanning tunneling microscope

Abstract: A Photon Scanning Tunneling Microscope (PSTM) with probe-sample distance control by electron tunneling is used to probe the localized surface-plasmon fields of individual nanometric silver particles. As samples, conventional island films produced by thermal evaporation and regular particle arrays produced by an electron-beam-lithography-based technique, respectively, are used. In either case the strength and spatial localization of the surface-plasmon fields strongly depend on the excitation wavelength. The results are interpreted as different resonance frequencies of individual particles or of different sample areas. On regular arrays consisting of particles with a smallest diameter of 40 nm, the PSTM maps represent the plasmon field strength spatially resolved for individual particles.

Optical second-harmonic generation of metal-island films

Abstract: In metal-island films consisting of nanometer particles on a transparent substrate irradiated light fields can be locally enhanced by electron-plasma resonances. Therefore, nonlinear optical processes should be enhanced dramatically. However, second-order nonlinear processes as second-harmonic generation occuring in the surface are strongly reduced by the centrosymmetric shape of the metal particles. It is found that this surface-specific contribution to second-harmonic generation is less enhanced, as is expected from the field enhancement. The “bulk” contribution, at smooth metal surfaces known to be much weaker than the contribution from the “real surface”, is strongly enhanced by the plasma resonances without symmetry restrictions and becomes comparably important.

Interference enhanced surface Raman scattering of adsorbates on a silver-spacer-islands multilayer system

Abstract: The intensity of surface Raman scattering from molecules adsorbed to a silver island film placed on top of a silver mirror, with an interlying quartz spacer layer of variable height, is found to vary considerably with spacer thickness. For quartz thicknesses up to 150 nm, the modulation of the Raman intensity is distinctly different for excitation by blue/green light from an Ar+ laser and by red light from a Kr+ laser. For Ar+ excitation, the Raman intensity peaks at (40 ± 20) nm quartz thickness, reaches minimum values between 90 nm and 120 nm, and increases again at higher thicknesses. In contrast, for Kr+ excitation the intensity decreases monotonically from its peak around ≈ 30 nm towards higher quartz thicknesses. The observed phenomena are discussed in terms of stratified medium theory. Thereby, the adsorbate layer does not need to be considered explicitly for sub-monolayer coverage; the excitation of localized surface plasmons in the island film is accounted for in the form of an effective dielectr...

Metal island coated polymer sensor for direct determination of the volume effect of chaotropic agents

Abstract: A new optical sensor is presented, based on the analyte reaction resulting in swelling and shrinking of a thin polymer layer. Changing the concentration of ions in a new bisazide photo-cross-linked poly(vinylpyrrolidone) polymer results in a concentration-dependent volume change of the hydrated gel. The volume response of the sensor induced by different ions is fully reversible over more than 250 cycles. The response of the device depends on the type, the charge and the concentration of the ions. The sensor material is part of an optical thin film system which transforms the variations in volume of the polymer into spectral information. The steady state of the sensor response is obtained within 60 s. The response time is mainly limited by the pump rate, the back pressure and the total volume of the system but not by the swelling of the sensor polymer. A comparative study of ion effects has demonstrated a fundamental correlation of the polymer swelling properties with the ‘Hofmeister series’ of chaotropic agents. Thus it is concluded that the photopolymer, which is solubilized in aqueous solutions by the interaction of its amide structure with the solvent, behaves like the backbone amide structure of proteins.

Optochemical sensor and process for its production

Abstract: An opto-chemical sensor with a reactive sensor layer for measuring concns. of substances has a reflecting layer (2), a reactive pref. swellable matrix (4) and a layer (3) with many "islands" (5) of electrically conductive material, pref. metal, the dia. of the islands being smaller than the wavelength of the light used for observation and/or analysis. Also claimed is a process for the prodn. of the sensor, in which the island film is produced on the polymer matrix (4) by vapour deposition, or produced or modified by attaching metal particles to (4), or produced or modified (in no. and size) by removing excess metal from (4). Pref. matrix (4) consists of optically transparent polymer, e.g. polyacrylic acid or PVP derivs., pref. acrylic acid/acrylamide copolymers. The optical thickness of this matrix is less than 1000 nm, pref. less than 600 nm.

New urea sensor based on a metal island coated ion sensitive swelling polymer device

Abstract: An optical reflectivity change induced by a change of the micro environment around metal island is used to construct various sensors and biosensors. To obtain a sensitive micro sensor either the island density at the surface of the sensor device or the distance of an island layer film to a solid metal surface or to another island film can be varied. Polyvinylpyrrolidone crosslinked with sulfonated bisazidostilbenes shows chaotropic ion dependent nanometric shrinking and swelling which can be observed by using this polymer as interlayer in a metal island device. This volume change of the sensing polymer is transduced to an optical signal using a metal island film, followed by a thin layer of an optically transparent welling polymer and a further metal island film as the topmost layer, exposed to the analyte. This new set-up enables the spectroscopic monitoring of the reflectance change from the backside of the sensor chip not exposed to the analyte solution. For the construction of a biosensor the device was either covered by a photo-structured polyvinylpyrrolidone membrane incorporating the desired enzymes or combined with a micro enzyme reactor. The fully reversible response of the sensor is induced by carbonate and ammonium ions liberated from urea by immobilized urease.

Near field optical investigations on nanometric silver particles

Abstract: A Photon Scanning Tunneling Microscope (PSTM) with a distance control by electron tunneling is used to probe the localised surface plasmon fields of individual nanometric silver particles. The samples are conventionally thermally evaporated “island” films as well as regular particle arrays produced by an electron beam lithography based technique. In either case the strength and spatial distribution of the localised plasmon fields strongly depend on the excitation wavelengths. These results are interpreted by different individual resonance frequencies of different sample areas or individual particles. On regular arrays, consisting of particles with a smallest diameter of 80 nm, the PSTM maps represent the plasmon field strength spatially resolved for individual particles.