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search.filters.applied.f.access: openAccess × End date: 2022 × End date: 2019 × Start date: 2010 × DDC: 600 × Type: Article × WGL Institute: IPHT ×

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Now showing 1 - 10 of 21
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    Propagating Surface Plasmon Polaritons: Towards Applications for Remote-Excitation Surface Catalytic Reactions
    (Weinheim : Wiley-VCH, 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.
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    Preparation of Core-Shell Hybrid Materials by Producing a Protein Corona Around Magnetic Nanoparticles
    (New York, NY [u.a.] : Springer, 2015) Weidner, A.; Gräfe, C.; von der Lühe, M.; Remmer, H.; Clement, J.H.; Eberbeck, D.; Ludwig, F.; Müller, R.; Schacher, F.H.; Dutz, S.
    Nanoparticles experience increasing interest for a variety of medical and pharmaceutical applications. When exposing nanomaterials, e.g., magnetic iron oxide nanoparticles (MNP), to human blood, a protein corona consisting of various components is formed immediately. The composition of the corona as well as its amount bound to the particle surface is dependent on different factors, e.g., particle size and surface charge. The actual composition of the formed protein corona might be of major importance for cellular uptake of magnetic nanoparticles. The aim of the present study was to analyze the formation of the protein corona during in vitro serum incubation in dependency of incubation time and temperature. For this, MNP with different shells were incubated in fetal calf serum (FCS, serving as protein source) within a water bath for a defined time and at a defined temperature. Before and after incubation the particles were characterized by a variety of methods. It was found that immediately (seconds) after contact of MNP and FCS, a protein corona is formed on the surface of MNP. This formation led to an increase of particle size and a slight agglomeration of the particles, which was relatively constant during the first minutes of incubation. A longer incubation (from hours to days) resulted in a stronger agglomeration of the FCS incubated MNP. Quantitative analysis (gel electrophoresis) of serum-incubated particles revealed a relatively constant amount of bound proteins during the first minutes of serum incubation. After a longer incubation (>20 min), a considerably higher amount of surface proteins was determined for incubation temperatures below 40 °C. For incubation temperatures above 50 °C, the influence of time was less significant which might be attributed to denaturation of proteins during incubation. Overall, analysis of the molecular weight distribution of proteins found in the corona revealed a clear influence of incubation time and temperature on corona composition.
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    Optical Properties of Silicon Nanowires Fabricated by Environment-Friendly Chemistry
    (New York, NY [u.a.] : Springer, 2016) Gonchar, Kirill A.; Zubairova, Alsu A.; Schleusener, Alexander; Osminkina, Liubov A.; Sivakov, Vladimir
    Silicon nanowires (SiNWs) were fabricated by metal-assisted chemical etching (MACE) where hydrofluoric acid (HF), which is typically used in this method, was changed into ammonium fluoride (NH4F). The structure and optical properties of the obtained SiNWs were investigated in details. The length of the SiNW arrays is about 2 μm for 5 min of etching, and the mean diameter of the SiNWs is between 50 and 200 nm. The formed SiNWs demonstrate a strong decrease of the total reflectance near 5-15 % in the spectral region λ < 1 μm in comparison to crystalline silicon (c-Si) substrate. The interband photoluminescence (PL) and Raman scattering intensities increase strongly for SiNWs in comparison with the corresponding values of the c-Si substrate. These effects can be interpreted as an increase of the excitation intensity of SiNWs due to the strong light scattering and the partial light localization in an inhomogeneous optical medium. Along with the interband PL was also detected the PL of SiNWs in the spectral region of 500-1100 nm with a maximum at 750 nm, which can be explained by the radiative recombination of excitons in small Si nanocrystals at nanowire sidewalls in terms of a quantum confinement model. So SiNWs, which are fabricated by environment-friendly chemistry, have a great potential for use in photovoltaic and photonics applications.
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    Nonresonant Raman spectroscopy of isolated human retina samples complying with laser safety regulations for in vivo measurements
    (Bellingham, Wash. : SPIE, 2019) Stiebing, Clara; Schie, Iwan W.; Knorr, Florian; Schmitt, Michael; Keijzer, Nanda; Kleemann, Robert; Jahn, Izabella J.; Jahn, Martin; Kiliaan, Amanda J.; Ginner, Laurin; Lichtenegger, Antonia; Drexler, Wolfgang; Leitgeb, Rainer A.; Popp, Jürgen
    Retinal diseases, such as age-related macular degeneration, are leading causes of vision impairment, increasing in incidence worldwide due to an aging society. If diagnosed early, most cases could be prevented. In contrast to standard ophthalmic diagnostic tools, Raman spectroscopy can provide a comprehensive overview of the biochemical composition of the retina in a label-free manner. A proof of concept study of the applicability of nonresonant Raman spectroscopy for retinal investigations is presented. Raman imaging provides valuable insights into the molecular composition of an isolated ex vivo human retina sample by probing the entire molecular fingerprint, i.e., the lipid, protein, carotenoid, and nucleic acid content. The results are compared to morphological information obtained by optical coherence tomography of the sample. The challenges of in vivo Raman studies due to laser safety limitations and predefined optical parameters given by the eye itself are explored. An in-house built setup simulating the optical pathway in the human eye was developed and used to demonstrate that even under laser safety regulations and the above-mentioned optical restrictions, Raman spectra of isolated ex vivo human retinas can be recorded. The results strongly support that in vivo studies using nonresonant Raman spectroscopy are feasible and that these studies provide comprehensive molecular information of the human retina. © The Authors. Published by SPIE.
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    Wet-chemical Passivation of Anisotropic Plasmonic Nanoparticles for LSPR-sensing by a Silica Shell
    (Amsterdam [u.a.] : Elsevier, 2015) Thiele, Matthias; Götz, Isabell; Trautmann, Steffen; Müller, Robert; Csáki, Andrea; Henkel, Thomas; Fritzsche, Wolfgang
    Metal nanoparticles showing the effect of localized surface plasmon resonance (LSPR), a collective oscillation of the conduction electrons upon interaction with light, represent an interesting tool for bioanalytics. This resonance is influenced by changes in the environment, and can be therefore used for the detection of molecular layers. The sensitivity, this means the extent of wavelength resonance shift per change in refractive index in the environment, represents an important performance parameter. It is higher for silver compared to gold particles, and is also increased for anisotropic particles. So silver triangles show a high potential for highly sensitive plasmonic nanoparticles. However, the stability under ambient conditions is rather poor. The paper demonstrates the passivation of silver triangles by silica coating using a wet-chemical approach. It compares the sensitivity for particles with and without passivation, and visualizes the passivation effect in a high resolution, single particle TEM study.
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    Spatial resolution of tip-enhanced Raman spectroscopy – DFT assessment of the chemical effect
    (Cambridge : RSC Publ., 2016) Latorre, Federico; Kupfer, Stephan; Bocklitz, Thomas; Kinzel, Daniel; Trautmann, Steffen; Gräfe, Stefanie; Deckert, Volker
    Experimental evidence of extremely high spatial resolution of tip-enhanced Raman scattering (TERS) has been recently demonstrated. Here, we present a full quantum chemical description (at the density functional level of theory) of the non-resonant chemical effects on the Raman spectrum of an adenine molecule mapped by a tip, modeled as a single silver atom or a small silver cluster. We show pronounced changes in the Raman pattern and its intensities depending on the conformation of the nanoparticle–substrate system, concluding that the spatial resolution of the chemical contribution of TERS can be in the sub-nm range.
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    Surface- and tip-enhanced Raman spectroscopy reveals spin-waves in iron oxide nanoparticles
    (Cambridge : RSC Publ., 2015) Rodriguez, Raul D.; Sheremet, Evgeniya; Deckert-Gaudig, Tanja; Chaneac, Corinne; Hietschold, Michael; Deckert, Volker; Zahn, Dietrich R. T.
    Nanomaterials have the remarkable characteristic of displaying physical properties different from their bulk counterparts. An additional degree of complexity and functionality arises when oxide nanoparticles interact with metallic nanostructures. In this context the Raman spectra due to plasmonic enhancement of iron oxide nanocrystals are here reported showing the activation of spin-waves. Iron oxide nanoparticles on gold and silver tips are found to display a band around 1584 cm−1 attributed to a spin-wave magnon mode. This magnon mode is not observed for nanoparticles deposited on silicon (111) or on glass substrates. Metal–nanoparticle interaction and the strongly localized electromagnetic field contribute to the appearance of this mode. The localized excitation that generates this mode is confirmed by tip-enhanced Raman spectroscopy (TERS). The appearance of the spin-waves only when the TERS tip is in close proximity to a nanocrystal edge suggests that the coupling of a localized plasmon with spin-waves arises due to broken symmetry at the nanoparticle border and the additional electric field confinement. Beyond phonon confinement effects previously reported in similar systems, this work offers significant insights on the plasmon-assisted generation and detection of spin-waves optically induced.
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    A manual and an automatic TERS based virus discrimination
    (Cambridge : RSC Publ., 2015) Olschewski, Konstanze; Kämmer, Evelyn; Stöckel, Stephan; Bocklitz, Thomas; Deckert-Gaudig, Tanja; Zell, Roland; Cialla-May, Dana; Weber, Karina; Deckert, Volker; Popp, Jürgen
    Rapid techniques for virus identification are more relevant today than ever. Conventional virus detection and identification strategies generally rest upon various microbiological methods and genomic approaches, which are not suited for the analysis of single virus particles. In contrast, the highly sensitive spectroscopic technique tip-enhanced Raman spectroscopy (TERS) allows the characterisation of biological nano-structures like virions on a single-particle level. In this study, the feasibility of TERS in combination with chemometrics to discriminate two pathogenic viruses, Varicella-zoster virus (VZV) and Porcine teschovirus (PTV), was investigated. In a first step, chemometric methods transformed the spectral data in such a way that a rapid visual discrimination of the two examined viruses was enabled. In a further step, these methods were utilised to perform an automatic quality rating of the measured spectra. Spectra that passed this test were eventually used to calculate a classification model, through which a successful discrimination of the two viral species based on TERS spectra of single virus particles was also realised with a classification accuracy of 91%.
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    Aqueous Black Colloids of Reticular Nanostructured Gold
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Stanca, S.E.; Fritzsche, W.; Dellith, J.; Froehlich, F.; Undisz, A.; Deckert, V.; Krafft, C.; Popp, J.
    Since ancient times, noble gold has continuously contributed to several aspects of life from medicine to electronics. It perpetually reveals its new features. We report the finding of a unique form of gold, reticular nanostructured gold (RNG), as an aqueous black colloid, for which we present a one-step synthesis. The reticules consist of gold crystals that interconnect to form compact strands. RNG exhibits high conductivity and low reflection and these features, coupled with the high specific surface area of the material, could prove valuable for applications in electronics and catalysis. Due to high absorption throughout the visible and infrared domain, RNG has the potential to be applied in the construction of sensitive solar cells or as a substrate for Raman spectroscopy.
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    Propagating and localized surface plasmon resonance sensing — A critical comparison based on measurements and theory
    (Amsterdam [u.a.] : Elsevier, 2016) Jatschka, Jacqueline; Dathe, André; Csáki, Andrea; Fritzsche, Wolfgang; Stranik, Ondrej
    With its potential for ultrasensitive, label-free detection of molecular interactions, sensing methods based on the surface plasmon resonance (SPR) effect fully meet the requirements for modern analytical techniques. Already established by using propagating SPR in thin gold layers, the last years witnessed the emergence of another related technique utilizing extremely miniaturized noble metal sensor structures, based on a localized SPR. This paper provides a critical comparison of these kinds of SPR sensing, reviews the foundation of both general approaches, presents experimental data on exactly the same molecular model system using both techniques, as well as theoretical considerations in order to allow reasonable comparison. It highlights the specific features and effects, in order to provide guidance in choosing the right technique for given bioanalytical tasks. The study demonstrated the capabilities of LSPR for sensing of molecular layers even in the lower nanometer dimension. For the detection of small (bio)molecules, smaller particle diameters are favored regarding highest sensitivity. It also presents an approach to obtain refractive index and the thickness of a molecular film by analyzing the signal response of plasmonic sensors with metal nanoparticles. Moreover, an additional method for the improvement of the parameters' determination is introduced.