2015, Faez, Sanli, Lahini, Yoav, Weidlich, Stefan, Garmann, Rees F., Wondraczek, Katrin, Zeisberger, Matthias, Schmidt, Markus A., Orrit, Michel, Manoharan, Vinothan N.

High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber having a subwavelength, nanofluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylindrical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions-26 nm in size and 4.6 megadaltons in mass-at rates of over 3 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.

2015, Zhang, Zhenglong, Fang, Yurui, Wang, Wenhui, Chen, Li, Sun, Mengtao

Plasmonics is a well-established field, exploiting the interaction of light and metals at the nanoscale; with the help of surface plasmon polaritons, remote-excitation can also be observed by using silver or gold plasmonic waveguides. Recently, plasmonic catalysis was established as a new exciting platform for heterogeneous catalytic reactions. Recent reports present remote-excitation surface catalytic reactions as a route to enhance the rate of chemical reactions, and offer a pathway to control surface catalytic reactions. In this review, we focus on recent advanced reports on silver plasmonic waveguide for remote-excitation surface catalytic reactions. First, the synthesis methods and characterization techniques of sivelr nanowire plasmonic waveguides are summarized, and the properties and physical mechanisms of plasmonic waveguides are presented in detail. Then, the applications of plasmonic waveguides including remote excitation fluorescence and SERS are introduced, and we focus on the field of remote-excitation surface catalytic reactions. Finally, forecasts are made for possible future applications for the remote-excitation surface catalysis by plasmonic waveguides in living cells.

2014, Auguste, J.-L., Humbert, G., Leparmentier, S., Kudinova, M., Martin, P.-O., Delaizir, G., Schuster, K., Litzkendorf, D.

The objective of this paper is to demonstrate the interest of a consolidation process associated with the powder-in-tube technique in order to fabricate a long length of specialty optical fibers. This so-called Modified Powder-in-Tube (MPIT) process is very flexible and paves the way to multimaterial optical fiber fabrications with different core and cladding glassy materials. Another feature of this technique lies in the sintering of the preform under reducing or oxidizing atmosphere. The fabrication of such optical fibers implies different constraints that we have to deal with, namely chemical species diffusion or mechanical stress due to the mismatches between thermal expansion coefficients and working temperatures of the fiber materials. This paper focuses on preliminary results obtained with a lanthano-aluminosilicate glass used as the core material for the fabrication of all-glass fibers or specialty Photonic Crystal Fibers (PCFs). To complete the panel of original microstructures now available by the MPIT technique, we also present several optical fibers in which metallic particles or microwires are included into a silica-based matrix.

2015, Nielsen, K.H., Wondraczek, K., Schubert, U.S., Wondraczek, L.

We report on a facile procedure for synthesis of nanoporous coatings of tungstic silica through wet-chemical deposition and post-treatment of tungsten-doped potassium silicate solutions. The process relies on an aqueous washing and ion exchange step where dispersed potassium salt deposits are removed from a 150 nm silicate gel layer. Through an adjustment of the pH value of the washing agent within the solubility regime of a tungstic salt precursor, the tungsten content of the remaining nanostructured coating can be controlled. We propose this route as a universal approach for the deposition of large-area coatings of nanoporous silica with the potential for incorporating a broad variety of other dopant species. As for the present case, we observe, on the one hand, antireflective properties which enable the reduction of reflection losses from float glass by up to 3.7 percent points. On the other hand, the incorporation of nanoscale tungstic precipitates provides a lever for tailoring the coating hydrophilicity and, eventually, also surface acidity. This may provide a future route for combining optical performance with anti-fouling functionality.

2014, Schwenkbier, Lydia, Pollok, Sibyll, König, Stephan, Urban, Matthias, Werres, Sabine, Cialla-May, Dana, Weber, Karina, Popp, Jürgen

Rapid detection and accurate identification of plant pathogens in the field is an ongoing challenge. In this study, we report for the first time on the development of a helicase-dependent isothermal amplification (HDA) in combination with on-chip hybridization for the detection of selected Phytophthora species. The HDA approach allows efficient amplification of the yeast GTP-binding protein (Ypt1) target gene region at one constant temperature in a miniaturized heating device. The assay's specificity was determined by on-chip DNA hybridization and subsequent silver nanoparticle deposition. The silver deposits serve as stable endpoint signals that enable the visual as well as the electrical readout. Our promising results point to the direction of a near future on-site application of the combined techniques for a reliable detection of Phytophthora species.

2014, Meyer-Ilse, J., Bauroth, S., Bräutigam, M., Schmitt, M., Popp, J., Beckert, R., Rockstroh, N., Pilz, T.D., Monczak, K., Heinemann, F.W., Rau, S., Dietzek, B.

The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand were investigated. The nitrogens on the bibenzimidazole-ligand were protected, by adding either a phenylene group or a 1,2-ethandiyl group, to remove the photophysical dependence of the complex on the protonation state of the bibenzimidazole ligand. This protection results in the bibenzimidazole ligand contributing to the MLCT transition, which is experimentally evidenced by (resonance) Raman scattering in concert with DFT calculations for a detailed mode assignment in the (resonance) Raman spectra.

2014, Kobelke, J., Bierlich, J., Wondraczek, K., Aichele, C., Pan, Z., Unger, S., Schuster, K., Bartelt, H.

All-solid microstructured optical fibers (MOF) allow the realization of very flexible optical waveguide designs. They are prepared by stacking of doped silica rods or canes in complex arrangements. Typical dopants in silica matrices are germanium and phosphorus to increase the refractive index (RI), or boron and fluorine to decrease the RI. However, the direct interface contact of stacking elements often causes interrelated chemical reactions or evaporation during thermal processing. The obtained fiber structures after the final drawing step thus tend to deviate from the targeted structure risking degrading their favored optical functionality. Dopant profiles and design parameters(e.g., the RI homogeneity of the cladding) are controlled by the combination of diffusion and equilibrium conditions of evaporation reactions. We show simulation results of diffusion and thermal dissociation in germanium and fluorine doped silica rod arrangements according to the monitored geometrical disturbances in stretched canes or drawn fibers. The paper indicates geometrical limits of dopant structures in sub-μm-level depending on the dopant concentration and the thermal conditions during the drawing process. The presented results thus enable an optimized planning of the preform parameters avoiding unwanted alterations in dopant concentration profiles or in design parameters encountered during the drawing process.

2015, Alexander Schmidt, Markus, Argyros, Alexander, Sorin, Fabien

The field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.

2015, Zhang, Zhenglong, Deckert-Gaudig, Tanja, Singh, Pushkar, Deckert, Volker

Surface plasmons on isolated gold dimers can initiate intermolecular reactions of adsorbed p-nitrothiophenol. At the single molecule level when dimerization is not possible an intramolecular reaction can be observed. Experimental evidence indicates that plasmon-induced hot electrons provide the required activation energy.

2014, Matthäus, C., Cicchi, R., Meyer, T., Lattermann, A., Schmitt, M., Romeike, B.F.M., Krafft, C., Dietzek, B., Brehm, B.R., Pavone, F.S., Popp, J.

Cardiovascular diseases in general and atherothrombosis as the most common of its individual disease entities is the leading cause of death in the developed countries. Therefore, visualization and characterization of inner arterial plaque composition is of vital diagnostic interest, especially for the early recognition of vulnerable plaques. Established clinical techniques provide valuable morphological information but cannot deliver information about the chemical composition of individual plaques. Therefore, spectroscopic imaging techniques have recently drawn considerable attention. Based on the spectroscopic properties of the individual plaque components, as for instance different types of lipids, the composition of atherosclerotic plaques can be analyzed qualitatively as well as quantitatively. Here, we compare the feasibility of multimodal nonlinear imaging combining two-photon fluorescence (TPF), coherent anti-Stokes Raman scattering (CARS) and second-harmonic generation (SHG) microscopy to contrast composition and morphology of lipid deposits against the surrounding matrix of connective tissue with diffraction limited spatial resolution. In this contribution, the spatial distribution of major constituents of the arterial wall and atherosclerotic plaques like elastin, collagen, triglycerides and cholesterol can be simultaneously visualized by a combination of nonlinear imaging methods, providing a powerful label-free complement to standard histopathological methods with great potential for in vivo application.