Search Results
Dehydroabietylamine-Based Cellulose Nanofibril Films: A New Class of Sustainable Biomaterials for Highly Efficient, Broad-Spectrum Antimicrobial Effects
2019, Hassan, Ghada, Forsman, Nina, Wan, Xing, Keurulainen, Leena, Bimbo, Luis M., Johansson, Leena-Sisko, Sipari, Nina, Yli-Kauhaluoma, Jari, Zimmermann, Ralf, Stehl, Susanne, Werner, Carsten, Saris, Per E.J., Österberg, Monika, Moreira, Vânia M.
The design of antimicrobial surfaces as integral parts of advanced biomaterials is nowadays a high research priority, as the accumulation of microorganisms on surfaces inflicts substantial costs on the health and industry sectors. At present, there is a growing interest in designing functional materials from polymers abundant in nature, such as cellulose, that combine sustainability with outstanding mechanical properties and economic production. There is also the need to find suitable replacements for antimicrobial silver-based agents due to environmental toxicity and spread of resistance to metal antimicrobials. Herein we report the unprecedented decoration of cellulose nanofibril (CNF) films with dehydroabietylamine 1 (CNF-CMC-1), to give an innovative contact-active surface active against Gram-positive and Gram-negative bacteria including the methicillin-resistant S. aureus MRSA14TK301, with low potential to spread resistance and good biocompatibility, all achieved with low surface coverage. CNF-CMC-1 was particularly effective against S. aureus ATCC12528, causing virtually complete reduction of the total cells from 10 5 colony forming units (CFU)/mL bacterial suspensions, after 24 h of contact. This gentle chemical modification of the surface of CNF fully retained the beneficial properties of the original film, including moisture buffering and strength, relevant in many potential applications. Our originally designed surface represents a new class of ecofriendly biomaterials that optimizes the performance of CNF by adding antimicrobial properties without the need for environmentally toxic silver. © Copyright 2019 American Chemical Society.
Characterization and effect of Ag(0) vs. Ag(I) species and their localized plasmon resonance on photochemically inactive TiO 2
2019, Handoko, Chanel Tri, Moustakas, Nikolaos G., Peppel, Tim, Springer, Armin, Oropeza, Freddy E., Huda, Adri, Bustan, Muhammad Djoni, Yudono, Bambang, Gulo, Fakhili, Strunk, Jennifer
Commercial TiO 2 (anatase) was successfully modified with Ag nanoparticles at different nominal loadings (1%-4%) using a liquid impregnation method. The prepared materials retained the anatase structure and contained a mixture of Ag 0 and Ag I species. Samples exhibited extended light absorption to the visible region. The effect of Ag loading on TiO 2 is studied for the photocatalytic reduction of CO 2 to CH 4 in a gas-solid process under high-purity conditions. It is remarkable that the reference TiO 2 used in this work is entirely inactive in this reaction, but it allows for studying the effect of Ag on the photocatalytic process in more detail. Only in the case of 2% Ag/TiO 2 was the formation of CH 4 from CO 2 observed. Using different light sources, an influence of the localized surface plasmon resonance (LSPR) effect of Ag is verified. A sample in which all Ag has been reduced to the metallic state was less active than the respective sample containing both Ag 0 and Ag + , indicating that a mixed oxidation state is beneficial for photocatalytic performance. These results contribute to a better understanding of the effect of metal modification of TiO 2 in photocatalytic CO 2 reduction. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
Gold-reinforced silver nanoprisms on optical fiber tapers - A new base for high precision sensing
2016, Wieduwilt, Torsten, Zeisberger, M., Thiele, M., Doherty, B., Chemnitz, M., Csaki, A., Fritzsche, W., Schmidt, M.A.
Due to their unique optical properties, metallic nanoparticles offer a great potential for important applications such as disease diagnostics, demanding highly integrated device solutions with large refractive index sensitivity. Here we introduce a new type of monolithic localized surface plasmon resonance (LSPR) waveguide sensor based on the combination of an adiabatic optical fiber taper and a high-density ensemble of immobilized gold-reinforced silver nanoprisms, showing sensitivities up to 900 nm/RIU. This result represents the highest value reported so far for a fiber optic sensor using the LSPR effect and exceeds the corresponding value of the bulk solution by a factor of two. The plasmonic resonance is efficiently excited via the evanescent field of the propagating taper mode, leading to pronounced transmission dips (−20 dB). The particle density is so high (approx. 210 particle/μm2) that neighboring particles are able to interact, boosting the sensitivity, as confirmed by qualitative infinite element simulations. We additionally introduce a qualitative model explaining the interaction of plasmon resonance and taper mode on the basis of light extinction, allowing extracting key parameters of the plasmonic taper (e.g., modal attenuation). Due to the monolithic design and the extremely high sensitivity we expect our finding to be relevant in fields such as biomedicine, disease diagnostics, and molecular sensing.
Highly sensitive and specific detection of E. coli by a SERS nanobiosensor chip utilizing metallic nanosculptured thin films
2015, Srivastava, Sachin K., Hamo, Hilla Ben, Kushmaro, Ariel, Marks, Robert S., Grüner, Christoph, Rauschenbach, Bernd, Abdulhalim, Ibrahim
A nanobiosensor chip, utilizing surface enhanced Raman spectroscopy (SERS) on nanosculptured thin films (nSTFs) of silver, was shown to detect Escherichia coli (E. coli) bacteria down to the concentration level of a single bacterium. The sensor utilizes highly enhanced plasmonic nSTFs of silver on a silicon platform for the enhancement of Raman bands as checked with adsorbed 4-aminothiophenol molecules. T-4 bacteriophages were immobilized on the aforementioned surface of the chip for the specific capture of target E. coli bacteria. To demonstrate that no significant non-specific immobilization of other bacteria occurs, three different, additional bacterial strains, Chromobacterium violaceum, Paracoccus denitrificans and Pseudomonas aeruginosa were used. Furthermore, experiments performed on an additional strain of E. coli to address the specificity and reusability of the sensor showed that the sensor operates for different strains of E. coli and is reusable. Time resolved phase contrast microscopy of the E. coli-T4 bacteriophage chip was performed to study its interaction with bacteria over time. Results showed that the present sensor performs a fast, accurate and stable detection of E. coli with ultra-small concentrations of bacteria down to the level of a single bacterium in 10 μl volume of the sample.
Towards on-site testing of Phytophthora species
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.
Development and Application of Efficient Ag‐based Hydrogenation Catalysts Prepared from Rice Husk Waste
2021, Unglaube, Felix, Kreyenschulte, Carsten Robert, Mejía, Esteban
The development of strategies for the sustainable management and valorization of agricultural waste is of outmost importance. With this in mind, we report the use of rice husk (RH) as feedstock for the preparation of heterogeneous catalysts for hydrogenation reactions. The catalysts were prepared by impregnating the milled RH with a silver nitrate solution followed by carbothermal reduction. The composition and morphology of the prepared catalysts were fully assessed by IR, AAS, ICP-MS, XPS, XRD and STEM techniques. This novel bio-genic silver-based catalysts showed excellent activity and remarkable selectivity in the hydrogenation of nitro groups in both aromatic and aliphatic substrates, even in the presence of reactive functionalities like halogens, carbonyls, borate esters or nitriles. Recycling experiments showed that the catalysts can be easily recovered and reused multiple times without significant drop in performance and without requiring re-activation. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH
Local protonation control using plasmonic activation
2001, Singh, P., Deckert, V.
Localized protonation of 4-mercaptopyridine (4-MPY), activated by light in the presence of silver nanoparticles is monitored under ambient conditions using surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS). The reaction can be controlled by the excitation wavelength and the atmospheric conditions, thus, providing a tool for site-specific control of protonation.
2D/3D Metallic Nano-objects Self-Organized in an Organic Molecular Thin Film
2020, Molodtsova, Olga V., Aristova, Irina M., Potorochin, Dmitrii V., Babenkov, Sergey V., Khodos, Igor I., Molodtsov, Serguei L., Makarova, Anna A., Smirnov, Dmitry A., Aristov, Victor Yu.
We present the fabrication and investigation of the properties of nanocomposite structures consisting of two-dimensional (2D) and three-dimensional (3D) metallic nano-objects self-organized on the surface and inside of organic molecular thin-film copper tetrafluorophthalocyanine (CuPcF4). Metallic atoms, deposited under ultrahigh vacuum (UHV) conditions onto the organic ultrathin film, diffuse along the surface and self-assemble into a system of 2D metallic overlayers. At the same time, the majority of the metal atoms diffuse into the organic matrix and self-organize into 3D nanoparticles (NPs) in a well-defined manner. The evolution of the morphology and electronic properties of such structures as a function of nominal metal content is studied under UHV conditions using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), and photoelectron spectroscopy (PES) techniques. Using HR-TEM, we have observed the periodicity of atomic planes of individual silver NPs. The steady formation of agglomerates from individual single nanocrystallites with intercrystallite boundaries is observed as well. PES reveals generally weak chemical interactions between silver and the organic matrix and n-doping of CuPcF4 at the initial stages of silver deposition, which is associated with charge transfer from the 2D wetting layer on the basis of core-level spectra shift analysis. Copyright © 2020 American Chemical Society.
Evaluation of colloids and activation agents for determination of melamine using UV-SERS
2012, Kämmer, E., Dörfer, T., Csáki, A., Schumacher, W., Da Costa Filho, P.A., Tarcea, N., Fritzsche, W., Rösch, P., Schmitt, M., Popp, J.
UV-SERS measurements offer a great potential for environmental or food (detection of food contaminats) analytics. Here, the UV-SERS enhancement potential of various kinds of metal colloids, such as Pd, Pt, Au, Ag, Au-Ag core-shell, and Ag-Au core-shell with different shapes and sizes, were studied using melamine as a test molecule. The influence of different activation (KF, KCl, KBr, K 2SO 4) agents onto the SERS activity of the nanomaterials was investigated, showing that the combination of a particular nanoparticle with a special activation agent is extremely crucial for the observed SERS enhancement. In particular, the size dependence of spherical nanoparticles of one particular metal on the activator has been exploited. By doing so, it could be shown that the SERS enhancement increases or decreases for increasing or decreasing size of a nanoparticle, respectively. Overall, the presented results demonstrate the necessity to adjust the nanoparticle size and the activation agent for different experiments in order to achieve the best possible UV-SERS results.
The morphology of silver nanoparticles prepared by enzyme-induced reduction
2012, Schneidewind, H., Schüler, T., Strelau, K.K., Weber, K., Cialla, D., Diegel, M., Mattheis, R., Berger, A., Möller, R., Popp, J.
Silver nanoparticles were synthesized by an enzyme-induced growth process on solid substrates. In order to customize the enzymatically grown nanoparticles (EGNP) for analytical applications in biomolecular research, a detailed study was carried out concerning the time evolution of the formation of the silver nanoparticles, their morphology, and their chemical composition. Therefore, silvernanoparticle films of different densities were investigated by using scanning as well as transmission electron microscopy to examine their structure. Cross sections of silver nanoparticles, prepared for analysis by transmission electron microscopy were additionally studied by energy-dispersive X-ray spectroscopy in order to probe their chemical composition. The surface coverage of substrates with silver nanoparticles and the maximum particle height were determined by Rutherford backscattering spectroscopy. Variations in the silver-nanoparticle films depending on the conditions during synthesis were observed. After an initial growth state the silver nanoparticles exhibit the so-called desert-rose or nanoflower-like structure. This complex nanoparticle structure is in clear contrast to the auto-catalytically grown spherical particles, which maintain their overall geometrical appearance while increasing their diameter. It is shown, that the desert-rose-like silver nanoparticles consist of single-crystalline plates of pure silver. The surface-enhanced Raman spectroscopic (SERS) activity of the EGNP structures is promising due to the exceptionally rough surface structure of the silver nanoparticles. SERS measurements of the vitamin riboflavin incubated on the silver nanoparticles are shown as an exemplary application for quantitative analysis.