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Antimicrobial peptides (AMP) are essential components of innate immunity with a broad range of antimicrobial activities against bacteria, viruses, and fungi. The aim of this study was to investigate AMP expression in the upper gastrointestinal tract in normal and pathological metabolic states in humans. Furthermore, we examined the correlation between vitamin D levels and AMP expression in the same cohort. Serum concentrations of 25-hydroxyvitamin D3 were measured, and mRNA expression of β-defensins HBD-1, -2, -3, -4, α-defensins HD-5 and -6 and cathelicidin in the upper gastrointestinal tract epithelia were determined by quantitative RT-PCR in 31 individuals (10 with type 2 diabetes, 10 with insulin resistance, and 11 healthy controls). The majority of the cohort showed low vitamin D concentrations, which were negatively correlated with mRNA expression levels of HBD-3 in corpus mucosa. HBD-1 and HBD-3 mRNA were expressed in corpus mucosa, with the former significantly decreased in patients with diabetes. Hence, we conclude that type 2 diabetes is associated with reduced AMP expression in the upper gastrointestinal tract, which might contribute towards epithelial barrier dysfunction and increased bacterial translocation in these patients.

Metal-organic framework (MOF) thin films are promising materials for multiple technological applications, such as chemical sensing. However, one potential limitation for their widespread use in different settings is their stability in aqueous environments. In the case of ZIF-8 (zeolitic imidazolate framework) thin films, their stability in aqueous media is currently a matter of debate. Here, we show that optical waveguide spectroscopy (OWS), in combination with surface plasmon resonance (SPR) spectroscopy, offers a convenient way for answering intriguing questions related to the stability of MOF thin films in aqueous solutions and, eventually provide a tool for assessing changes in MOF layers under different environmental conditions. Our experiments relied on the use of ZIF-8 thin films grown on surface-modified gold substrates, as optical waveguides. We have found a linear thickness increase after each growing cycle and observed that the growing characteristics are strongly influenced by the nature of the primer layer. One of our findings is that substrate surface modification with a 3-mercapto-1-propanesulfonate (MPSA) primer layer is critical to achieve ZIF-8 layers that can effectively act as optical waveguides. We observed that ZIF-8 films are structurally stable upon exposure to pure water and 50 mM NaCl solutions but they exhibit a slight swelling and an increase in porosity probably due to the permeation of the solvent in the intergrain mesoporous cavities. However, OWS revealed that exposure of ZIF-8 thin films to phosphate-buffered saline solutions (pH 8) promotes significant film degradation. This poses an important question as to the prospective use of ZIF-8 materials in biologically relevant applications. In addition, it was demonstrated that postsynthetic polyelectrolyte modification of ZIF-8 films has no detrimental effects on the structural stability of the films. Fil: Allegretto, Juan Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de San Martín; Argentina Fil: Dostalek, Jakub. Austrian Institute Of Technology; Austria Fil: Rafti, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Menges, Bernhard. Resonant Technologies GmbH; Alemania Fil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Knoll, Wolfgang. Austrian Institute Of Technology; Austria

On-surface chemistry for atomically precise sp2 macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp2-carbon nanometer-thin films on insulators and under ultrahigh vacuum (UHV) conditions from photocoupled brominated precursors. We reveal that covalent coupling is initiated by C–Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C–Br scission and C–C coupling processes. Further, unreacted material can be sublimed and the coupled sp2-carbon precursors can be graphitized by e-beam treatment at 500 °C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp2-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology., We acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374) Spanish Grants (FIS2010-21282-C02-01 and PIB2010US-00652), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), Ikerbasque and the European Commission projects CRONOS (Grant 280879-2 CRONOS CP-FP7). C.-A.P. and K.D. were funded through the ERC Advanced Grant MolArt (no. 247299). D.J.M. acknowledges funding through the Spanish “Juan de la Cireva” program (JCI-2010-08156). J.L.C acknowledges funding through the Mexican CONACyT program.

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers plasma polymers as homogeneous and continuous structures. Refereed/Peer-reviewed

We have investigated thick films from polybutadiene on gold-coated glass using surface plasmon resonance / leaky optical waveguide spectroscopy with the aim of investigating differences in bulk and interphase properties in a single measurement. A broad range of molar masses was studied. Drying under ambient conditions leads to an exponential decay of the film thickness. Subsequent vacuum drying does not result in any further changes in the bulk part of the film but at the polymer-solid interface, indicating the absence of residual solvent. For all molar masses studied, the surface plasmon resonance is observed at angles which are incompatible with the properties of the bulk part of the film. A polymer interphase is thus present next to the gold layer which has a refractive index lower than in the bulk. Using transversal magnetic- and transversal electric polarized light, an optical anisotropy is found in the interphase which is attributed to segment alignment along the interface with gold.

Fluorescence quenching is a powerful technique used to obtain information about the dynamic changes of proteins in complex macromolecular systems. In this work, graphene is shown to be a very efficient quencher of fluorescence molecules where the quenching effect was one order of magnitude higher than that of gold. The fluorescence intensity was distance-dependent where increasing the distance between the fluorescence molecule and the graphene surface from 4 to 7 nm increased the fluorescence intensity by a factor of 7.5. This type of distance dependence suggests a nonradiative nature in the energy transfer between the graphene and the fluorophore due to the excitation of an exciton.

Interfaces and interphases are a vital part of everyday life—since the influence of their proximity might change considerably the behaviour of systems studied. The ability to study motion on the nanometre scale is essential for the understanding of transport phenomena to and from surfaces, thin films or membranes. It is indispensable to have analytical methods with spatio-temporal resolution adapted to these problems and which are non-invasive to obtain untainted results. The small dimensions lead to weak signals and therefore we need experimental setups which are able to amplify them. Here we describe a dynamic light scattering experiment where the evanescent part of waveguide modes is used as the source of light. Using waveguide modes increased the signal-to-noise ratio by a factor of 8 compared to evanescent waves generated by total internal reflection and it allows adjusting the spatial resolution near the interface in situ. This technique monitors changes of the waveguide surface as e.g. adsorption to it.

Polymer-supported bilayer lipid membranes offer great opportunities for the investigation of functional membrane proteins. Here we present a new approach in this direction by introducing a thin hydrogel layer as a soft ‘cushion’ on indium–tin oxide (ITO), providing a smooth, functional surface to form the protein-tethered BLM (ptBLM). ITO was used as a transparent electrode, enabling simultaneous implementation of electrochemical and optical waveguide techniques. The hydrogel poly(N-(2-hydroxyethyl)acrylamide-co-5-acrylamido-1-carboxypentyl-iminodiacetate-co-4-benzoylphenyl methacrylate) (P(HEAAm-co-NTAAAm-co-MABP)) was functionalized with the nickel chelating nitrilotriacetic acid (NTA) groups, to which cytochrome c oxidase (CcO) from Paracoccus denitrificans was bound in a well defined orientation via a his-tag attached to its subunit I. Given that the mesh size of P(HEAAm-co-NTAAAm-co-MABP) was smaller than the protein size, binding to the hydrogel occurred only on the top of the layer. The lipid bilayer was formed around the protein by in situdialysis. Electrochemical impedance spectroscopy showed good electrical sealing properties with a resistance of ∼1 MΩ cm2. Furthermore, surface plasmon resonance optical waveguide spectroscopy (SPR/OWS) indicated an increased anisotropy of the system after formation of the lipid bilayer. Cyclic voltammetry in the presence of reduced cytochrome c demonstrated that CcO was incorporated into the gel-supported ptBLM in a functionally active form.

Optical waveguide spectroscopy has been used to study the real-time adsorption of ruthenium 535-bisTBA (N-719) dye in mesoporous nanocrystalline titanium dioxide films of the type used in dye-sensitized solar cells (DSCs). Porous titania films were prepared on top of gold substrates, and prism coupling was used to create a guided wave in the nanocrystalline film. The conditions under which a guided mode can be excited are dependent on both the refractive index and the extinction coefficient of the mesoporous layer, where the mesoporous layer refers to both the nanocrystals of TiO2 and the composition of the pores. It was therefore possible to track changes in dye concentration in the pores in real time. The total concentration of dye in the film appeared to continue increasing even after 22 h, in contrast to the amount of dye in the pores that was able to absorb light at 632.8 nm, which saturated after ∼5 h. The total concentration of dye molecules was 2.47 × 10−4 mol cm−3 as a function of the total pore ...

Thin films of plasma polymerized pentafluorophenyl methacrylate (pp-PFM) offer highly reactive ester groups throughout the structure of the film that allow for subsequent reactions with different aminated reagents and biological molecules. The present paper follows on from previous work on the plasma deposition of pentafluorophenyl methacrylate (PFM) for optimum functional group retention (Francesch, L.; Borros, S.; Knoll, W.; Foerch, R. Langmuir 2007, 23, 3927) and reactivity in aqueous solution (Duque, L.; Queralto, N.; Francesch, L.; Bumbu, G. G.; Borros, S.; Berger, R.; Förch, R. Plasma Process. Polym. 2010, accepted for publication) to investigate the binding of a biologically active peptide known to induce cellular adhesion (IKVAV) and of biochemically active proteins such as BSA and fibrinogen. Analyses of the films and of the immobilization of the biomolecules were carried out using infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The attachment of the biomolecules on pulsed plasma polymerized pentafluorophenyl methacrylate was monitored using surface plasmon resonance spectroscopy (SPR). SPR analysis confirmed the presence of immobilized biomolecules on the plasma polymer and was used to determine the mass coverage of the peptide and proteins adsorbed onto the films. The combined analysis of the surfaces suggests the covalent binding of the peptide and proteins to the surface of the pp-PFM.

Surface-attached, photo-crosslinked gel films of a N-isopropylacrylamide copolymer were investigated in ethanol/water mixtures using a combination of surface plasmon resonance/ optical waveguide spectroscopy with reversed WKB analysis. The solvent quality of the pure good solvents drops in their mixture and this co-nonsolvency effect shifts the transition temperature (T c ) in the μm-thin gel films from 32.8 °C in pure water to 29.7 °C with only 0.25 vol.-% ethanol. Between 20 and 70% ethanol and >10 °C (the practical temperature limit) the layers existed only in the collapsed state. A reentrant T c of 40.2 °C was found at 70% ethanol while at higher ethanol volume fraction no T c could be recorded.

Langmuir–Blodgett (LB) films of side chain polyamic acids were formed, deposited onto optical waveguides and imidized via heating to the corresponding polyimides on the optical waveguides. The LB film formation of the side chain polyamic acids, the imidization reaction and the glass transition behaviour of the polyimide thin films were investigated. Polarisation dependent waveguide mode spectroscopy was applied therefore. It was found that the glass transition temperature (Tg) of bulk and LB thin film samples of these polymers are identical and only depend on the spacer length between the side chain and backbone, not on film thickness. Our investigation shows that in the case of the ultrathin film geometry, the glass transition temperature exhibits an anisotropic behaviour. We find the classical kink in the temperature scan (a change in slope of the free volume vs. temperature plot) due to the thermal expansion change at Tg, in p-polarisation only, which is perpendicular to the main chain orientation. In the s-polarisation measurements (parallel to the main chains) no kink was found, only an offset in the vicinity of Tg. We attribute the anisotropic thermal behaviour to a transition, the freezing of segmental motion, in the side chains only.

A new sensor for the thermo-optical detection of surface plasmon resonance (SPR) is presented. The sensor incorporates a grating coupler, patterned in a thin noble metal film (Au or Ag, respectively) for excitation of SPR by monochromatic laser light and a thin film thermal sensor for detection of the temperature change by absorbed radiation power. High sensitivity of the sensor is obtained by micromechanical patterning of a thin membrane area below the sensitive metal film. Design optimization has been performed by FEM simulations. First results regarding the thermal detection of SPR during the formation of supramolecular architectures on a silver film are presented. The measurements are compared with the results, obtained with conventional optical sensor devices.

To generate command surfaces for all-optical switching, highly ordered polymeric Langmuir-Blodgett-Kuhn (LBK) multilayers were fabricated onto silicon substrates and gold-coated optical glass slides from novel azobenzene-bearing polyamic acid systems. Pronounced Bragg peaks and well-defined Kiessig fringes observed in the X-ray reflectivity measurement for samples on silicon substrates indicate that these films possess a regularly repeated Y-type LBK multilayer structure and ultrasmooth surfaces. Fourier transform infrared (FT-IR) spectra taken by grazing incidence reflection suggest specific orientations of the functional groups in the layers. The excellent film-forming properties of the polyamic acid allow for a smooth buildup of several hundreds of layers of the LBK films onto gold-coated glass slides, which in turn allows for determining the geometrical thickness and the anisotropic refractive indices of the films by using optical waveguide spectroscopy. Interestingly, the probe laser beam induced a distinct fluorescence signal from the films, which remained even after the film underwent a thermal imidization process at 160 degrees C for 8 h in vacuo. LBK films fabricated from these compounds can be successfully applied for all-optically switching the alignment of liquid crystals by irradiation with light of different wavelengths.

The coupling of p-polarized waveguide modes into waveguide-surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons and the unique possibility to functionalize the metal surface by self-assembled monolayers (SAMs) via sulfur chemistry. Recently we have demonstrated a waveguide device which allows to couple two TM waveguide modes to the surface plasmon and were able to characterize a new binding matrix with respect to the thickness and the refractive index. The noise and the sensitivity of this device needs further improvement. Therefore we present a sensitivity and device realizability study in order to optimize the technique of multimode waveguide mode surface plasmon coupling for the determination of the thickness and the refractive index of ultrathin layers binding to a metal surface.

Photosensitive mesoionic polymers in which the polymerizable methacrylic group is attached to the malonic acid component of the mesoionic function were prepared and characterized. Dielectric measurements were performed, and the results were compared to those of liquid-crystalline mesoionic copolymers. The influence on the dielectric properties upon irradiation with UV light, which causes the photoconversion of the mesoionic groups to bis(β-lactame) structures, was determined. The glass-transition temperatures determined by dielectric spectroscopy were compared to those obtained by DSC. It could be observed by waveguide-mode spectroscopy that irradiating the mesoionic methacrylates results in remarkable effects on the film thickness and refractive index of spin-coated polymer films.

This study deals with the synthesis of a polyphenol bearing photosensitive groups, and its photochemical behavior upon UV irradiation. Mesoionic 5-(4-hydroxybenzyl)-6-oxo-1,2,3-triphenyl-1,6-dihydropyrimidin-3-ium-4-olate was prepared by condensation of 4-benzyloxybenzylmalonic acid with N,N'-diphenylbenzamidine using dicyclohexylcarbodiimide as condensing agent, followed by deprotection of the benzyl group. The monomer was polymerized by an iron-salen complex to give a polymer with a mesoionic 6-oxo-1,6-dihydropyridimin-3-ium-4-olate moiety as the pendant group. Spin coated polymer films were prepared and characterized. It was shown by IR spectroscopy structure to a bis(β-lactam) structure. Waveguide spectroscopy showed a large decrease in the film thickness without refractive index changes during irradiation.

The attachment of fibrinogen, bovine serum albumin, and immunoglobulin on continuous wave (CW) and pulsed plasma polymerized di(ethylene glycol) monovinyl ether was studied using surface plasmon resonance (SPR) spectroscopy and waveguide mode spectroscopy (WaMS). Structural analysis of the films was carried out using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Plasma conditions employed during depositions produced significant differences in the chemical and physical properties of the resultant polymer films. Films deposited under CW and higher plasma duty cycles showed relatively high refractive indices (n > 1.57) and essentially a constant thickness if immersed in aqueous buffer solutions and exhibited a high adsorption affinity for proteins. In contrast, films produced under lower plasma duty cycles were of lower refractive index (n < 1.4), exhibited significant swelling if immersed in aqueous buffer, and were extremely effective in preventing ...

A polymeric amidine prepared by melt condensation was converted to a photosensitive polymesoion by a polymer analogous condensation reaction with methylmalonic acid. The polymeric mesoion was characterized by NMR, IR, and UV spectroscopies; SEC; and DSC. For investigation of optical properties, spin-coated films were prepared and analyzed by waveguide spectroscopy. It was found that the refractive index shows anisotropic changes and that the film thickness was reduced upon irradiation as a result of conversion to a poly-bis(β-lactame) structure.

A new method for in-situ film characterisation during thin film deposition processes was developed using waveguide mode spectroscopy. The advantages of the method are a high sensitivity for thin films in the nm-regime and a relatively simple and low-cost set-up. The detection method relies on a double grating coupler allowing a background-free detection of the propagation constants of guided optical modes. The set-up is based on a reflected mode m-line geometry requiring no moving parts. The method was applied to thin film diagnostics in plasma-assisted deposition processes and allowed for the simultaneous determination of thickness and refractive index of the plasma polymer film during deposition. The in-situ waveguide mode spectrometer was also used to monitor gas phase reactions of plasma polymerised maleic anhydride thin films on-line.

Various vinylbenzaldehydes were prepared using the Heck reaction: 4-vinylbenzaldehyde (14), 3-vinylbenzaldehyde (15), 2-vinylbenzaldehyde (18a), 2-hydroxy-4-vinylbenzaldehyde (16) and 4-[(4-vinylbenzyl)oxy]benzaldehyde (6). The four monomers (6, 14, 15, 16) were polymerized using AIBN as initiator at 70 °C for 24 h to yield the corresponding homopolymers (7, 19, 23, 25) and a copolymer (20) with styrene. The molecular weights are about 10 000. The polymer analogous condensation of the aldehyde groups with an excess of N-isopropylhydroxylamine (8) at room temperature produces polymeric nitrons (9, 21, 22, 24, 26) in almost quantitative yields. All nitron functions were irradiated, and the intramolecular cyclization of the nitrons to the corresponding oxaziridines was examined. Waveguide mode spectroscopy of poly(4-vinylbenzaldehyde-N-isopropylnitron) (21) shows that the changes in film thickness are low but the changes in refractive indices are significant after irradiation. Oxaziridine 10 has high therma...

A functionalized biotin compound is synthesized and assembled on a graphene surface where the electrical and optical properties of graphene are retained. Surface plasmon resonance spectroscopy (amo...

An in situ determination of the optical properties of films deposited during plasma polymerisation processes with nanometer accuracy has been realised using waveguide mode spectroscopy. The detection method relies on a bi-diffractive grating coupler with two grating constants and allows the background free detection of the propagation constants in a reflected mode geometry. It enables separate determination of the refractive index (n) and the thickness (d) as the plasma polymer film grows. The method has been applied in a preliminary study of the plasma assisted deposition mechanism of allylamine and maleic anhydride.

The formation of the base pair adenine-uracil at a water−solid interface, at an immobilized monolayer of adenine disulfide with adenine groups exposed to the very surface, respectively, is shown here. To overcome the steric hindrance of tightly packed adenine groups in a pure adenine thiolate monolayer on gold, the formation of self-assembled monolayers out of a binary mixture of the adenine disulfide and CH3- or OH-terminated thiols are investigated. Electro-chemical investigations, surface plasmon spectroscopy (PSP, plasmon surface polariton), multimode waveguide-PSP-coupling spectroscopy, contact angle measurements, and spontaneous desorption time-of-flight mass spectrometry were used to characterize the monolayers. The specific base pairing was investigated for a variety of monolayer compositions. A specific base pairing was successful for an optimized mixed adenine/OH-terminated thiol monolayer. Nevertheless unspecific binding is a problem.

The coupling of p-polarized waveguide modes into waveguide-surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons. We demonstrate a waveguide device which allows to couple two TM modes to the surface plasmon. For a given waveguide device and a fixed laser wavelength the development of the imaginary part, κ, of the propagation constant, Neff, of the waveguide-surface plasmon coupled modes are simulated to optimize a monolayer sensitive device. The waveguide attenuation is very sensitive to the refractive index architecture within the evanescent field of these combined modes. This resonant behavior was used to measure the refractive index and the geometrical thickness of self-assembled monolayers independently from each other. In addition the binding of uracil to a binary monolayer containing adenin was investigated.

Amine-functionalized thin films were prepared by plasma-induced deposition of allylamine. Radio frequency (rf) plasma polymerization was carried out under both continuous wave (CW) and pulsed conditions to control the film chemistry. The chemical and physical nature of plasma-polymerized allylamine films was investigated, as well as the effect of solvent treatment on the structure of the polymeric material. The film properties were studied using Waveguide Mode Spectroscopy (WaMS), which enabled an independent determination of film thickness and refractive index. Fourier transform infrared (FTIR) spectroscopy showed that changes in duty cycle led to different film chemistries. WaMS carried out on thin films (d < 60 nm) showed changes in the refractive index with increasing thickness believed to suggest intermolecular reactions occurring in the bulk while the film is depositing. All films studied showed a significant loss of soluble material from the surface upon solvent extraction. After extraction however, the films were stable and could be reversibly swollen in ethanol.

We investigated the fluorescence in Na + →Ag + -ion exchanged BK7 glass slab waveguides. The waveguide characteristics, the refractive index profile and the losses were measured. The index profile could be described by a nonlinear diffusion equation. The fluorescence, due to colloidal silver particles, increases with increasing ion exchange time and with decreasing wavelength of the guided light. In addition, the waveguide surface was plasma treated by ion glow discharge and an enhancement of fluorescence was observed with increasing discharge time. Most of the fluorescence light does not couple into waveguide modes and can therefore be used to measure the losses surface scattering free.

We study the possibilities for photopatterning a polymethylmethacrylate derivative carrying an anthracene group in the side chain. This material allows the preparation of high quality optical films by spin coating. Upon irradiation of these films with UV light changes in the optical constants, refractive index and absorption, and the degree of solubility can be induced by photocrosslinking and endoperoxide formation. These features qualify this polymer as a promising material for both integrated optics and photolithography or a combination of both.

This paper describes a simple and sensitive immuno-based biosensor for interference-reduced detection of C-reactive protein (CRP) in serum. The detection was performed by using a non-competitive sandwich immunoassay in combination with surface plasmon field-enhanced fluorescence spectroscopy (SPFS). CRP is an important marker for the diagnosis of inflammatory processes and cardiovascular diseases (CVD). It is nowadays detected by high-sensitivity enzyme-linked immunosorbent assays (ELISA) in blood serum. CRP was used as a model analyte in this work because it is well-characterized. However, interfering effects of matrix components affect the limit of detection (LOD) and quantification (LOQ) in general. Therefore, the availability of fast, sensitive and robust analytical methods is of major interest. A number of biosensor approaches have been described already, but only a few have demonstrated their usefulness in authentic samples such as serum. Thus our aim was to develop a simple and sensitive immunoassay-based biosensor for an interference-reduced detection of CRP in serum with surface plasmon enhanced fluorescence spectroscopy (SPFS). LODs and LOQs were experimentally determined both for CRP spiked buffer and serum. SPFS in combination with our biosensor allows sensitive analysis of CRP, achieving in buffer a LOD of 0.016 μg mL(-1) and a LOQ of 0.049 μg mL(-1). In serum the accomplished LOD was 0.026 μg mL(-1) and the LOQ was found to be 0.08 μg mL(-1). These low LODs and LOQs demonstrate the applicability of the designed biosensor for qualitative and semi-quantitative analysis of trace amounts of substances in very small sample volumes of body fluids.

We demonstrate a fast and simple technique of patterning insoluble, nonbleachable, conjugated polymer films into channel waveguides by striploading with photoresist. Two types of coupling gratings were tested for this new system. The coupling parameters, the linear losses and the beam confinement are discussed. This technique makes it possible to explore this class of materials in the field of integrated optics. A new data evaluation method for a more precise measurement of losses in slab waveguides is introduced.

We present a novel light scattering setup that enables probing of dynamics near solid surfaces. An evanescent wave generated by a surface plasmon resonance in a metal layer is the incident light field in the dynamic light scattering experiment. The combination of surface plasmon resonance spectroscopy and dynamic light scattering leads to a spatiotemporal resolution extending a few hundred nanometers from the surface and from microseconds to seconds. The comparison with evanescent wave dynamic light scattering identifies the advantages of the presented technique, e.g., surface monitoring, use of metal surfaces, and biorelevant systems. For both evanescent wave geometries, we define the scattering wave vector necessary for the analysis of the experimental relaxation functions.

Graphene, a newly discovered material with unusual electrical and optical properties, has attracted interest for a number of potential applications. One of the most actively pursued applications is using graphene as a transparent conducting electrode for use in solar cells, displays or touch screens. In this work, two studies are pursued in parallel to explore the electrical and optical properties of graphene. Graphene was prepared on copper by the standard chemical vapor deposition (CVD) method [1], the preparation procedure and conditions are described in [2]. The effect of chemical p-type doping on graphene stacks was studied in order to reduce the sheet resistance of graphene. The doping decreases the sheet resistance by a factor of 3, yielding films comprised of eight stacked layers with a sheet resistance of 90 Ω/ at a transmittance of 80% [2]. A theoretical model that accurately describes the stacked graphene film system as a resistor network was also developed [2]. The experimental data shows a linear increase in conductivity with the number of graphene layers, indicating that each layer provides an additional transport channel, in good agreement with the theoretical model (Fig. 1).

Surface-attached, cross-linked hydrogel films based on thermoresponsive N-isopropylacrylamide with a dry thickness >1 microm were studied with surface plasmon resonance/optical waveguide mode spectroscopy (SPR/OWS) to monitor temperature-dependent and salt-induced changes of their swelling state. In combination with the reversed Wentzel-Kramers-Brillouin and Bruggeman effective medium approximation and by modeling the hydrogel film as a composite of sublayers with individual complex refractive indices, refractive index/volume fraction gradient profiles perpendicular to the surface are accessible simultaneously with information about local inhomogeneities. Specifically, the imaginary refractive index kappa of each sublayer can be interpreted as a measure for static and dynamic inhomogeneities, which were found to be highest at the volume transition collapse temperature in the layer center. These results indicate that the hydrogel collapse originates rather from the film center than from its boundaries. Upon addition of NaCl to a swollen hydrogel below its transition temperature, comparable optical loss characteristics as for the thermal gel collapse are observed with respect to inhomogeneities. Interestingly, in contrast to the thermally induced layer shrinkage and collapse, swelling increases at intermediate salt concentrations.

This paper will present a new sensor device based on the simultaneous excitation of (p-polarized) waveguide modes and surface plasmon polaritons forming so-called guided hybrid-modes. These modes offer greater design flexibility and the potential for monolithic integration of the well-established technique of surface plasmon resonance (SPR). The sensor device consists of a metal-coated planar dielectric waveguide with an embossed shallow diffraction coupling grating and a flow cell on top. Various numerical simulations are presented to achieve optimum sensor parameters complemented by experimental checks of the predicted sensor properties. The experimental section includes the preparation of the sensor device together with measurements using different analyte-solutions, which modify the cladding properties of the sensor chip are presented. Measured reflectivity data of the hybrid-mode sensor are reported and compared to theoretical predictions.

This article reports the implementation of optical waveguide spectroscopy (OWS) for the quantitative time-resolved observation of changes in the swelling behavior and mass density of protein-functionalized hydrogel films. In the experiment, a thin film of an N-isopropylacrylamide (NIPAAm)-based polymer that supported optical waveguide modes is attached to a metallic sensor surface. IgG molecules are in situ immobilized in this gel by using novel coupling chemistry with a charge-attraction scheme based on a tetrafluorophenol sulfonate active ester. The anti-fouling properties of the functionalized hydrogel network and the kinetics of the affinity binding of protein molecules in the gel are investigated.

In this paper we will discuss a few basic concepts concerning the use of evanescent optical fields for the excitation of fluorescent chromophores placed near the interface. The observation of enhanced fluorescence from chromophores excited by surface plasmon and waveguide modes will be presented and discussed. We attribute the enhancement to the near-field interaction between the chromophores and the increased photonic mode density by surface plasmon and waveguide modes. We determined limits of detection (LOD) of DNA hybridisation using the same sensor architecture by surface plasmon fluorescence spectroscopy (SPFS) and optical waveguide fluorescence spectroscopy (OWFS). Both SPFS and OWFS techniques have the same detection principle using an enhanced electromagnetic field to excite fluorophores and make it possible to monitor DNA hybridisation in real-time with high sensitivity. The relative photonic mode density of each mode was calculated under the resonance condition, and these values are reflected in the LOD values.

The structural features and swelling properties of responsive hydrogel films based on poly(N-isopropylacrylamide) copolymers with a photo-cross-linkable benzophenone unit were investigated by surface plasmon resonance, optical waveguide mode spectroscopy, and atomic force microscopy. The temperature-dependent swelling behavior was studied with respect to the chemical composition of the hydrogel polymers containing either sodium methacrylate or methacrylic acid moieties. In the sodium methacrylate system, a refractive index gradient was found that was not present in the free acid gel. This refractive index gradient, perpendicular to the swollen hydrogel film surface, could be analyzed in detail by application of the reversed Wentzel-Kramers-Brillouin (WKB) approximation to the optical data. This novel approach to analyzing thin-film gradients with the WKB method presents a powerful tool for the characterization of inhomogeneous hydrogels, which would otherwise be very difficult to capture experimentally. In AFM images of the hydrogel layers, a macroscopic pore structure was observed that depended on the polymer composition as well as on the swelling history. This pore structure apparently prevents the often-observed skin barrier effect and leads to a quickly responding hydrogel.

The combination of various evanescent optical methods such as surface plasmon spectroscopy, waveguide mode spectroscopy and an integrated optical Mach-Zehnder-interferometer are used to characterize biotinylated self-assembled monolayers as well as the binding of streptavidin to these labels. The aim of designing a highly specific and sensitive, re-usable affinity sensor for antigens on the basis of an integrated optical Mach-Zehnder interferometer is based on a proper understanding of the characteristics of the entire binding matrix architecture. Therefore, a variety of biotin-derivatives immobilized in a monolayer are investigated with respect to their affinity to streptavidin and the possibility to remove the steptavidin layer specifically. The density of the streptavidin layer as well as the optical constants of the involved molecules are measured. Finally the integrated optical Mach-Zehnder interferometer is tested with respect to the sensitivity to an antigen-antibody binding reaction. An attempt to further increase the sensitivity by simultaneous detection of a fluorescence signal failed due to bleaching effects.

Scattering optical waveguide microscopy is a novel imaging technique, that allows for the microscopic characterization of thin film samples by using the evanescent field of a guided optical wave as the illuminating light source. The image contrast is generated by the scattered intensity of the thin film sample within the evanescent field. Excellent lateral resolution (< 1 micrometers ) is demonstrated for an evaporated SiOx grating. Immersion microscopy has been performed with an additional cuvette in the same setup. The contrast of the image is investigated with respect to mode number and polarization of the illuminating, propagating waveguide mode and the surface roughness of the sample.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The coupling of p-polarized waveguide modes into waveguide- surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons. We demonstrate a waveguide device which allows to couple more than one TM mode to the surface plasmon. For a given waveguide device and a fixed laser wavelength the development of the imaginary part, K, of the propagation constant, Neff, of the waveguide-surface plasmon coupled modes are simulated and the results are compared with experimental results. The waveguide losses are in perfect agreement with the simulations. Due to the resonant nature of the waveguide-surface plasmon coupled modes, which was found by the simulations, the waveguide attenuation is very sensitive to the refractive index of the subphase outside of the waveguide structure. This resonant behavior could be confirmed experimentally.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Amine-functionalized thin films were prepared by plasma induced deposition of allylamine. Radio frequency (rf) plasma polymerization was carried out under both continuous wave (CW) and pulsed plasma conditions to control the film chemistry, all other process variables being held constant. Using plasma polymerized films for subsequent grafting reactions or for direct biomedical applications usually involves exposure of the films to a solvent environment. It was the major focus of this work to investigate both the chemical and physical effects of solvents on plasma polymerized allylamine films. Film properties were determined using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Waveguide Mode Spectroscopy (WaMS) and Surface Plasmon Spectroscopy (SPS). WaMS provided an ideal opportunity to study the complex swelling and drying behaviour of these films by allowing a simultaneous study of the changes in film thickness and refractive index. Although the amine groups of the monomer were increasingly retained in the films as the RF duty cycle was lowered, a larger amount of oxygen was also found to be incorporated upon exposure to air. Extraction in ethanol led to a decrease in film thickness, especially for the films produced at low duty cycles, but appeared to have little effect on the film composition, as measured by XPS and FTIR.

New polymeric azines, DOZ and DOPh, containing the 3-dodecylthiophene moiety, have been obtained by the condensation reactions of 2,5-diformyl-3-dodecylthiophene with hydrazine and p-diaminobenzene, respectively. Their average molecular masses depend on the preparation conditions. Using DOZ polymers, which are completely soluble in common organic solvents, we were able to demonstrate channel waveguide formation and function. The waveguide losses could be separated into intrinsic absorption losses and scattering contributions.

Functional hydrogel films on solid supports are versatile materials with large potential for cell growth and tissue engineering. Here, we report on a modular approach to generate functional hydrogel composite films for endothelial and osteoblast cell co-culture. The polymer network of the parent hydrogel was formed by a dextran derivative (BP-CMD), which contained carboxymethyl (CM) groups for further chemical functionalization and benzophenone (BP) moieties as a photocrosslinkable unit. BP-CMD could be synthesized by three different routes, first with the benzophenone unit attached via an amide bond, or second by an ether bond, or third as an ion pair between the benzophenone ammonium salt and the carboxylate groups on the dextran backbone. For composite formation, BP-functionalized silica nanoparticles, as well as gelatin particles were mixed with BP-CMD and permanently fixed in the hydrogel matrix by photocrosslinking for mechanical reinforcement and to facilitate cell growth. In the last preparation step the BMP-2 growth factor was covalently coupled to the polymer backbone, which enhanced osteoblast and endothelial cell growth. The swelling behavior and successful BMP-2 immobilization of the hydrogel composite films were investigated with surface plasmon resonance and optical waveguide mode spectroscopy coupled with fluorescence detection. This modular approach allows independent selection and optimization of each component in the hydrogel composite for a wide range of potential applications for targeted cell growth, as successfully shown here with osteoblast–endothelial cell co-culture for bone tissue regeneration.

We employed fluorescence correlation spectroscopy to investigate the effect of crosslinking density, annealing in the dry state, temperature, and solvent quality on the one-dimensional swelling, permeability, and mobility of tracer molecules in thermoresponsive hydrogel films. These consist of a carboxylated poly(N-isopropylacrylamide) derivative (PNIPAAm) covalently anchored to glass substrates. Upon increasing the temperature beyond the collapse transition at about 32 °C, the gels shrunk from the swollen to a collapsed state. A molecular dye (Alexa 647) and green fluorescent protein were chosen as tracers as they display only weak interaction with the carboxylated PNIPAAm. At large swelling ratios (low temperatures) the hydrogel layers are spatially homogeneous and both tracers show single Fickian diffusion. Diffusion coefficients scale with the PNIPAAm volume fraction. Upon temperature increase a qualitatively different behavior is observed already in the pretransition region (25–32 °C) concurrently with moderate swelling ratios (

A new responsive nanocomposite material consisting of a poly-(N-isopropylacrylamide) hydrogel and “super-crosslinking” silica nanoparticles was prepared by mixing both components in solution, spincoating a thin film, and photocrosslinking by UV irradiation. Detailed analysis of the thermal response of these water-swollen films by means of surface plasmon resonance and optical waveguide spectroscopy revealed that the composite is very stable and has excellent responsive properties; it is of high optical homogeneity; admixture of the nanoparticles (up to 50%-wt) does not affect the critical volume collapse temperature; and swell-collapse cycles are highly reproducible and display only limited hysteresis. Thus, the composite is promising as a scaffold for further functionalisation and incorporation in sensors or actuators.

Experiments addressing supramolecular dynamics at interfaces are of paramount importance for the understanding of the dynamic behaviour of polymers, particles, or cells at interfaces, transport phenomena to and from surfaces, thin films or membranes. However, there are only few reports in the literature due to the paucity of experimental methods that offer the required spatial and time resolution. Evanescent wave dynamic light scattering originally developed to meet these needs has limited sensitivity and is restricted to glass substrates. Here we report the first experimental realization of a dynamic light scattering experiment close to an interface using surface plasmon polaritons as light source offering a strong increase in the signal to noise ratio and allowing for the use of metallic interfaces. As a proof of concept, we consider the diffusion of particles with radii down to 10nm in dilute dispersions close to a gold surface.