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- ItemSingle molecule level plasmonic catalysis – a dilution study of p-nitrothiophenol on gold dimers(Cambridge : Soc., 2015) Zhang, Zhenglong; Deckert-Gaudig, Tanja; Singh, Pushkar; Deckert, VolkerSurface 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.
- ItemA thiazolo[5,4-: D] thiazole-bridged porphyrin organic framework as a promising nonlinear optical material(London : Royal Society of Chemistry (RSC), 2019) Samal, Mahalaxmi; Valligatla, Sreeramulu; Saad, Nabil A.; Rao, M. Veeramohan; Rao, D. Narayana; Sahu, Rojalin; Biswal, Bishnu P.Porphyrin-based porous organic frameworks are an important group of materials gaining interest due to their structural diversity and distinct opto-electronic properties. However, these materials are seldom explored for nonlinear optical (NLO) applications. In this work, we investigate a thiazolo[5,4-d]thiazole-bridged porous, porphyrin framework (Por-TzTz-POF) with promising NLO properties. The planar TzTz moiety coupled with integrated porphyrin units enables efficient π-conjugation and charge distribution in the Por-TzTz-POF resulting in a high nonlinear absorption coefficient (β = 1100 cm GW-1) with figure of merit (FoM) σ1/σ0 = 5571, in contrast to analogous molecules and material counterparts e.g. metal-organic frameworks (MOFs; β = ∼0.3-0.5 cm GW-1), molecular porphyrins (β = ∼100-400 cm GW-1), graphene (β = 900 cm GW-1), and covalent organic frameworks (Por-COF-HH; β = 1040 cm GW-1 and FoM = 3534). This journal is © The Royal Society of Chemistry.
- ItemOberflächenmorphologie von Arzneistoffpartikeln - Ein optisch evaluierbares Kriterium für die Auflösungsgeschwindigkeit(München : Elsevier, Urban & Fischer , 2002) Diebold, Steffen M.Für die Auflösungsgeschwindigkeit von schwer wasserlöslichen Arzneistoffpartikeln spielt die Hydrodynamik an den Partikel-Oberflächen eine große Rolle. Diese ist ihrerseits beeinflußt von der Geometrie und der Oberflächenmorphologie der Partikel. In dieser Arbeit wurde gezeigt, dass sich zur Charakterisierung dieser Parameter die Rasterelektronenmikroskopie (SEM) auch für die Untersuchung von Arzneistoffen gut eignet. Am Beispiel von Felodipin-Kristallen wurde nachgewiesen, dass reale Arzneistoffpulver auch an scheinbar „glatten“ Oberflächen Protrusionen, Kanten und Kavitäten aufweisen. Deren Größenordnungen lassen sich mit Hilfe der Elektronenmikroskopie abschätzen. Die Oberflächenmorphologie von Arzneistoffpartikeln ist ein Kriterium für die Auflösungsgeschwindigkeit oral verabreichter Arzneistoffe. Die Rasterelektronenmikroskopie leistet dabei wertvolle Dienste zur Charakterisierung der Oberflächen von Arzneistoffpartikeln.
- ItemOn the stability of microwave-fabricated SERS substrates - chemical and morphological considerations(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2021) Wang, Limin; Womiloju, Aisha Adebola; Höppener, Christiane; Schubert, Ulrich Sigmar; Hoeppener, StephanieThe stability of surface-enhanced Raman spectroscopy (SERS) substrates in different organic solvents and different buffer solutions was investigated. SERS substrates were fabricated by a microwave-assisted synthesis approach and the morphological as well as chemical changes of the SERS substrates were studied. It was demonstrated that the SERS substrates treated with methanol, ethanol, or N,N-dimethylformamide (DMF) were comparable and showed overall good stability and did not show severe morphological changes or a strong decrease in their Raman activity. Toluene treatment resulted in a strong decrease in the Raman activity whereas dimethyl sulfoxide (DMSO) treatment completely preserved or even slightly improved the Raman enhancement capabilities. SERS substrates immersed into phosphate-buffered saline (PBS) solutions were observed to be rather instable in low and neutral pH buffer solutions. Other buffer systems showed less severe influences on the SERS activity of the substrates and a carbonate buffer at pH 10 was found to even improve SERS performance. This study represents a guideline on the stability of microwave-fabricated SERS substrates or other SERS substrates consisting of non-stabilized silver nanoparticles for the application of different organic solvents and buffer solutions.
- ItemSurface modification of the laser sintering standard powder polyamide 12 by plasma treatments(Weinheim : Wiley-VCH, 2018-6-7) Almansoori, Alaa; Masters, Robert; Abrams, Kerry; Schäfer, Jan; Gerling, Torsten; Majewski, Candice; Rodenburg, CorneliaPolyamide 12 (PA12) powder was exposed for up to 3 h to low pressure air plasma treatment (LP-PT) and several minutes by two different atmospheric pressure plasma jets (APPJ) i.e., kINPen (K-APPJ) and Hairline (H-APPJ). The chemical and physical changes resulting from LP-PT were observed by a combination of Scanning Electron Microscopy (SEM), Hot Stage Microscopy (HSM) and Fourier transform infrared spectroscopy (FTIR), which demonstrated significant changes between the plasma treated and untreated PA12 powders. PA12 exposed to LP-PT showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from the surface functionalization and materials removal during the plasma exposure. However, it showed poor melt behavior under heating conditions typical for Laser Sintering. In contrast, brief PJ treatments demonstrated similar changes in porosity, but crucially, retained the favorable melt characteristics of PA12 powder.
- ItemX-ray Ptychographic Imaging and Spectroscopic Studies of Plasma-Treated Plastic Films(Basel : MDPI, 2022) Ravandeh, Mehdi; Mehrjoo, Masoud; Kharitonov, Konstantin; Schäfer, Jan; Quade, Antje; Honnorat, Bruno; Ruiz-Lopez, Mabel; Keitel, Barbara; Kreis, Svea; Pan, Rui; Gang, Seung-gi; Wende, Kristian; Plönjes, ElkePolyethylene terephthalate (PET) is a thermoplastic polyester with numerous applications in industry. However, it requires surface modification on an industrial scale for printing and coating processes and plasma treatment is one of the most commonly used techniques to increase the hydrophilicity of the PET films. Systematic improvement of the surface modification by adaption of the plasma process can be aided by a comprehensive understanding of the surface morphology and chemistry. However, imaging large surface areas (tens of microns) with a resolution that allows understanding the surface quality and modification is challenging. As a proof-of-principle, plasma-treated PET films were used to demonstrate the capabilities of X-ray ptychography, currently under development at the soft X-ray free-electron laser FLASH at DESY, for imaging macroscopic samples. In combination with scanning electron microscopy (SEM), this new technique was used to study the effects of different plasma treatment processes on PET plastic films. The studies on the surface morphology were complemented by investigations of the surface chemistry using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). While both imaging techniques consistently showed an increase in roughness and change in morphology of the PET films after plasma treatment, X-ray ptychography can provide additional information on the three-dimensional morphology of the surface. At the same time, the chemical analysis shows an increase in the oxygen content and polarity of the surface without significant damage to the polymer, which is important for printing and coating processes.
- ItemLabel-free detection of Phytophthora ramorum using surface-enhanced Raman spectroscopy(Cambridge : Soc., 2015) Yüksel, Sezin; Schwenkbier, Lydia; Pollok, Sibyll; Weber, Karina; Cialla-May, Dana; Popp, JürgenIn this study, we report on a novel approach for the label-free and species-specific detection of the plant pathogen Phytophthora ramorum from real samples using surface enhanced Raman scattering (SERS). In this context, we consider the entire analysis chain including sample preparation, DNA isolation, amplification and hybridization on SERS substrate-immobilized adenine-free capture probes. Thus, the SERS-based detection of target DNA is verified by the strong spectral feature of adenine which indicates the presence of hybridized target DNA. This property was realized by replacing adenine moieties in the species-specific capture probes with 2-aminopurine. In the case of the matching capture and target sequence, the characteristic adenine peak serves as an indicator for specific DNA hybridization. Altogether, this is the first assay demonstrating the detection of a plant pathogen from an infected plant material by label-free SERS employing DNA hybridization on planar SERS substrates consisting of silver nanoparticles.