Harald Brunner

Enhanced dye fluorescence over silver island films: analysis of the distance dependence

Fluorescence intensity enhancement has been studied for several coverages (10-3 to 1 monolayer) of Rhodamine 6G separated from a silver island film by quartz spacer layers of varying thickness. When the dye film is brought into the proximity of the island film support, a first enhancement maximum is observed at ≈ 60 nm spacer thickness. For smaller distances, decrease in the enhancement is followed by a second maximum at 5–10 nm interlayer thickness. The magnitude of the latter maximum exhibits a pronounced dependence on dye coverage. The far-field enhancement maximum is due to an increase in fluorescence quantum yield induced by the presence of the island film substrate, combined with a resonant excitation phenomenon due to collective action of the islands. This effect is analysed in terms of stratified medium theory, in which the island film is represented by a suitable model for the effective dielectric constant. The short distance enhancement results from competition between the strongly amplified loc...

Optical properties of a metal island film close to a smooth metal surface

Bright colors have been observed when a metal island film is deposited on top of a silver mirror with a separating quartz layer. For spacer layer thicknesses that are varied from 0 to 140 nm, the visual appearance changes from blue/black to a series of brilliant spectrumlike colors. The sequence is repeated similarly for higher interlayer thicknesses. The phenomenon is analyzed in terms of a stratified medium theory by using TEM data and an electromagnetic model for the optical constants of the metal island film. For island films with a sufficiently high absorbance (> 0.35), the spectra are characterized by two sharp minima where the reflectivity drops to values below l0(-3). The observed thickness dependence is analyzed in terms of a complex combination of the phase shifts caused by the island film, the spacer, and the relevant interfaces.

Detection of fluorophore-labeled antibodies by surface-enhanced fluorescence on metal nanoislands

In fluorescence labelled immunosensing the discrimination of labels remaining in the bulk solution from labels bound to the analyte at the sensor surface is a basic optical problem. It is shown that application of surface enhanced fluorescence at a layer of noble metal nano-particles can increase the surface-to-background signal ratio. We explain the enhancement mechanism by an electrodynamic model and discuss the interaction between metal particle and fluorophore for the excitation and emission process. We show the principal guidelines for optimization of that processes. We find that the obtained discrimination power increases with decreasing intrinsic quantum efficiency of the fluorophore, suggesting the application of new classes of labels, namely low-quantum efficiency fluorophores. This theoretical finding is shown by a practical model experiment.

PICOSECOND DYNAMICS OF THE EXCITED STATE RELAXATIONS IN PHYTOCHROME

Abstract— A comparative study of the picosecond kinetics of rye (Secale cereale L.) phytochrome, its 39 and 23 kDa chromopeptides and deuterated rye phytochrome has been carried out. Evidence is presented that the fluorescence decay of Pr contains a very short lifetime component (14 ps) which has escaped detection in the fluorescence studies reported so far. Thus, the overall decay is well described by four exponential components, two rapid (14 and 44 ps) and two slower ones (157 and 690 ps). The fluorescence decays of deuterated Pr and of a 39 and 23 kDa chromopeptide of Pr also require the analysis in terms of four exponentials for a good fit. Some of the lifetime and amplitude values obtained differ significantly from the values estimated for Pr. In the chromopeptides, the two longer components have distinctly slower decays. For the two faster components the lifetimes remain approximately the same, but their relative amplitudes vary greatly. In deuterated Pr, the lifetimes are affected only slightly by deuteration. In contrast, the decay amplitudes are strikingly altered. Moreover, from a rate equation simulation modelling the observed fluorescence kinetics, it turns out that the yields for the various deactivation steps in the chromopeptides and in deuterated Pr reveal differences from the corresponding values in Pr. The implications of the results presented with respect to the influence of the protein moiety of Pr on the picosecond relaxation process are discussed.

Picosecond events in the phototransformation of phytochrome - a time-resolved absorption study?

Abstract Picosecond time-resolved transient absorption studies with phytochrome in its red light absorbing form (P r ) isolated from rye ( Secale cereale cv. Danae ) are reported. After excitation of P r with 6 ps pulses at 621 nm the transient absorption spectra were measured at various delay times from 5 ps up to 1 ns. Upon excitation an increase in the transient absorption around 400 nm immediately appeared, which is ascribed to the first excited state absorption of P r . With a delay of about 15 ps a strong bleaching of the P r ground state absorption around 665 nm emerged. After a series of further absorption changes, an increase in absorbance occurred above 685 nm. Since this transient absorption persisted over the 1 ns time-window measured, it is interpreted as being due to the formation of lumi-R. Based on the time evolution of the observed absorption changes it seems likely that two pools of lumi-R were formed. In addition, it was found from the kinetics of the picosecond absorption changes that the relaxation of excited P r obviously involves processes which follow a non-exponential rate law. From a comparison with picosecond adsorption spectroscopy on deuterated P r and a 39 kDa chromopeptide, conclusions about the first relaxation steps in the phototransformation of P r are drawn. It is suggested that they involve rotations at the single bonds in the chromophoric methine bridges.

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

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...

Enhanced second harmonic generation in a silver–spacer–islands multilayer system

Second harmonic radiation from a silver island film may be enhanced by two orders of magnitude in multilayer structures in which the film is placed on top of a silver mirror, with an interlying quartz spacer layer of variable height. The dependence of the enhancement on spacer thickness is distinctly different for s and p polarization of the fundamental beam; minimum enhancement for p‐polarized excitation coincides with an enhancement maximum for s polarization. The origin of this phenomenon is discussed in terms of stratified medium theory: It arises from an amplification of the field in the island film layer, as a consequence of coherent superposition of the multiply reflected partial waves. The excitation of localized surface plasmons in the island film is taken into account in terms of an effective dielectric constant. In agreement with symmetry arguments, the produced second harmonic radiation is predominantly p‐polarized, even for s‐polarized excitation. Good agreement between the model calculations...

Picosecond spectroscopy of dihydro biliverdin

Picosecond time-resolved fluorescence and absorption spectroscopy was performed on dihydro biliverdin, a model for the chromophore in the plant pigment phytochrome, a chromoprotein governing plant growth. Close agreement between the model compound and the native chromophore proves the importance of the saturated pyrrol ring for the decay kinetics and renders chromophore protonation in phytochrome unlikely.

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

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.

The greening process in cress seedlings IV. Light regulated expression of single Lhc genes

Abstract Transcript levels of single Lhc genes were determined in etiolated cress seedlings (Lepidium sativum L.) after various irradiations. Hybridization probes used in this study specifically detected transcripts of three Lhcb1 genes (probes cd1, cd2, cd3), one Lhcb2 gene (probe cd4), one Lhcb3 gene (probe cd5) and one Lhcb3 gene (probe 6). A 2 min pulse of red light resulted in a transient increase in the steady-state level of all transcripts determined for up to 10 h after the light pulse. Light induction was stronger in 4 day old than in 3 day old seedlings. The maximum of light induction was generally reached 4 h after a pulse of red light except for Lchb2 and Lchb3 transcripts that exhibited a maximum already 2 h after the light pulse. The relationship between red, blue and far-red irradiation was similar for all investigated Lhc genes: transcrip levels were 75–85% after a 30 min blue and 60–70% after a 30 min far-red pulse, compared with the red pulse = 100%. The contribution of the photoreceptor phytochrome and the physiological role of different kinetics of expression are discussed.