Influences on Plasmon Resonance Linewidth in Metal-Insulator-Metal Structures Obtained via Colloidal Self-Assembly.

Localized surface plasmon resonances (LSPRs) have been widely explored in various research fields because of their excellent ability to condense light into a nanometer scale volume. However, it suffers quite often from the broadening of the LSPR linewidths, resulting in low quality factors. Among the causes of the broadening, fabrication inaccuracies are crucial yet challenging to evaluate. In this paper, we designed a type of metal-insulator-metal structure as an example via the colloidal self-assembly approach. We then demonstrated a facile approach to identify the origin of the discrepancies in between spectra obtained from experiments and simulations. Through a series of simulations in accordance with the experimental results, we could confirm that the predominant influencing factors are the presence of defects, as well as feature size variations, though they impact the spectral response in different ways. For similar plasmonic systems, our results enabled a more cost-effective optimization process in lieu of rather intensive and iterative experimentations, which will pave the way to automated fabrication and optimization, as well as integrated design. Furthermore, our results also indicated that the typical defect ratio that is introduced via the colloidal self-assembly approach has only limited impact on the resulting plasmonic resonances, proving that for similar plasmonic structure designs, colloidal self-assembly methods can provide a reliable and efficient alternative in the field of nanofabrication of plasmonic systems.

Anisotropic Etching of Pyramidal Silica Reliefs with Metal Masks and Hydrofluoric Acid.

This work describes the fabrication of anisotropically etched, faceted pyramidal structures in amorphous layers of silicon dioxide or glass. Anisotropic and crystal-oriented etching of silicon is well known. Anisotropic etching behavior in completely amorphous layers of silicon dioxide in combination with purely isotropic hydrofluoric acid as etchant is an unexpected phenomenon. The work presents practical exploitations of this new process for self-perfecting pyramidal structures. It can be used for textured silica or glass surfaces. The reason for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. The lateral etch rate under the metal significantly exceeds the vertical etch rate of the non-metallized area by a factor of about 6-43 for liquid and 59 for vapor-based processes. The ratio between lateral and vertical etch rate, thus the sidewall inclination, can be controlled by etchant concentration and selected metal. The described process allows for direct fabrication of shallow angle pyramids, which for example can enhance the coupling efficiency of light emitting diodes or solar cells, can be exploited for producing dedicated silicon dioxide atomic force microscopy tips with a radius in the 50 nm range, or can potentially be used for surface plasmonics.

Stabilizing Alginate Confinement and Polymer Coating of CO-Releasing Molecules Supported on Iron Oxide Nanoparticles To Trigger the CO Release by Magnetic Heating.

Maghemite (Fe2O3) iron oxide nanoparticles (IONPs) were synthesized, modified with covalent surface-bound CO-releasing molecules of a tri(carbonyl)-chlorido-phenylalaninato-ruthenium(II) complex (CORM), and coated with a dextran polymer. The time- and temperature-dependent CO release from this CORM-3 analogue was followed by a myoglobin assay. A new measurement method for the myoglobin assay was developed, based on confining "water-soluble" polymer-coated Dextran500k@CORM@IONP particles in hollow spheres of nontoxic and easily prepared calcium alginate. Dropping a mixture of Dextran500k@CORM@IONP and sodium alginate into a CaCl2 solution leads to stable hollow spheres of Ca(2+) cross-linked alginate which contain the Dextran500k@CORM@IONP particles. This "alginate-method" (i) protects CORM-3 analogues from rapid CO-displacement reactions with a protein, (ii) enables a spatial separation of the CORM from its surrounding myoglobin assay with the alginate acting as a CO-permeable membrane, and (iii) allows the use of substances with high absorptivity (such as iron oxide nanoparticles) in the myoglobin assay without interference in the optical path of the UV cell. Embedding the CORM@IONP nanoparticles in the alginate vessel represents a compartmentation of the reactive component and allows for close contact with, yet facile separation from, the surrounding myoglobin assay. The half-life of the CO release from Dextran500k@CORM@IONP particles surrounded by alginate was determined to be 890 ± 70 min at 20 °C. An acceleration of the CO release occurs at higher temperature with a half-life of 172 ± 27 min at 37 °C and 45 ± 7 min at 50 °C. The CO release can be triggered in an alternating current magnetic field (31.7 kA m(-1), 247 kHz, 39.9 mT) through local magnetic heating of the susceptible iron oxide nanoparticles. With magnetic heating at 20 °C in the bulk solution, the half-life of CO release from Dextran500k@CORM@IONP particles decreased to 155 ± 18 min without a noticeable temperature increase in the dispersion. At 37 and 50 °C, the half-life for the CO release triggered by local magnetic heating was 65 ± 5 min and 30 ± 3 min, respectively. Thus, at a physiological temperature of 37 °C, magnetic heating accelerates the CO release of the IONP-bound CORM by a factor of ∼ 2.6. The activation energy for CO release from a CORM-3 analogue was determined to be EA = 78 kJ/mol.

Assessing the influence of diurnal variations and selective Xa inhibition on whole blood aggregometry.

A biological rhythm in platelet function is well known. Multiple electrode aggregometry (MEA) is a widely used assay to measure platelet aggregability. Rivaroxaban is a new oral anticoagulant frequently used in an increasing number of indications. In this randomized, crossover trial we investigated whether a biological rhythm exists in MEA measurements and potential effects of rivaroxaban on platelet aggregation. Sixteen healthy volunteers were included in the study and blood samples were obtained at 08:00, 12:00, 16:00 and 20:00 h. Each subject was tested without rivaroxaban intake first and randomly assigned to 3 days of rivaroxaban intake at 08:00 or 3 days of rivaroxaban intake at 20:00 h and vice versa. In MEA measurements, a significant increase in platelet aggregation after addition of ristocetin at 12:00 h compared to other investigated time-points (122 ± 8 AU at 12:00 h vs. 109 ± 9 AU at 08:00 h, 114 ± 10 AU at 16:00 h and 103 ± 8 AU at 20:00 h, p = 0.027) could be detected. There was no biological rhythm detectable using other agonists (ADP, arachidonic acid, thrombin-receptor activating peptide-6). After rivaroxaban intake at 08:00 h an increased ristocetin-induced platelet aggregation was measured in the next morning (126 ± 4 AU (rivaroxaban at 08:00 h) vs. 109 ± 9 AU (no rivaroxaban), 111 ± 6 AU (rivaroxaban at 20:00 h; p = 0.002). No other effects of rivaroxaban on platelet function were found. We detected a biological rhythm in ristocetin-induced platelet aggregation with a peak at 12:00 h (noon). No influence of selective Xa inhibition on platelet aggregation was detected.