Maas, Michael
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Item type:Publication, Arsenic and sulfur nanoparticle synthesis mimicking environmental conditions of submarine shallow-water hydrothermal vents(2022-01); ; ; Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter (OM) can influence the mobilization of the toxic metalloid in marine environments. In the present study we analyze the influence of temperature and OM (particularly sulfur-containing additives) on As and S precipitation based on the recent discovery of As-rich nanoparticles in the hydrothermal system near the coast of the Greek island Milos. To this end, we experimentally recreate the formation of amorphous colloidal particles rich in As and S via acidification (pH 3-4) of aqueous precursors at various temperatures. At higher temperatures, we observe the formation of monodisperse particles within the first 24 h of the experiment, generating colloidal particles with diameters close to 160 nm. The S:As ratio and particle size of the synthetized particles closely correlates with values for AsxSy particles detected in the hydrothermal system off Milos. Furthermore, organic sulfur containing additives (cysteine and glutathione, GSH) are a key factor in the process of nucleation and growth of amorphous colloidal AsxSy particles and, together with the temperature gradient present in shallow hydrothermal vents, dictate the stabilization of As-bearing nanomaterials in the environment. Based on these findings, we present a simple model that summarizes our new insights into the formation and mobility of colloidal As in aquatic ecosystems. In this context, amorphous AsxSy particles can present harmful effects to micro- and macro-biota not foreseen in bulk As material.Book137 112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, An evaluation of colloidal and crystalline properties of CaCO3 nanoparticles for biological applicationsBiodegradable calcium carbonate carriers are a promising and safe nanoparticle platform which might enable various applications as an engineered nanomaterial in health care, food and cosmetics. However, engineered nanoparticles can exhibit new forms of toxicity that must be carefully evaluated before being widely adopted in consumer products or novel drug delivery systems. To this end, we studied four common calcium carbonate particle systems (calcite nanoparticles, amorphous sub-micrometer and vaterite sub-micrometer and micrometer particles) and compared their behavior in biological medium and in cell culture experiments. The thermodynamically stable calcite phase is shown to maintain its morphological features as no phase transformation occurs. Size- and time-dependent phase transformation of the less stable vaterite particles are observed within 96h in cell medium. The protein serum albumin can be an effective inhibitor of phase-transition and it is shown to improve colloidal stability. The impact of the biological environment goes beyond protein-corona formation, as we observed rapid dissolution of amorphous particles in high ionic strength cell medium, but not in Millipore water. Cellular responses of human osteoblasts against CaCO3 particles indicate that increased intracellular calcium ions improve viability and that particle internalization is not size-dependent. Useful insights for designing CaCO3-based delivery systems are provided and also corroborate to the idea that intrinsic material properties as well as environmental conditions are of relevance for the successful implementation of dispersed CaCO3 particles in drug delivery systems and in other applications.journal articleBand:78103 212 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Proteolytic ceramic capillary membranes for the production of peptides under flow(Elsevier, 2019-04-15); ; ; ; In this study, we investigate the effect of membrane surface functionalization on the immobilization of the protease subtilisin A and its performance in the production of peptides from the model protein casein under flow. The surface of tubular ceramic membranes was silanized to yield carboxylated and aminated supports for enzyme immobilization via non-covalent and carbodiimide activated binding. The protease density correlated with electrostatic interactions between the positively charged enzyme and the supports, with the highest enzyme density reached on negatively charged, carboxylated membranes (0.019 molecules/nm², noncovalent approach). Enzyme leaching was reduced by covalent binding of protease to carboxylated supports (5% leached) and slightly improved by binding to aminated membranes (46%) over non-covalent binding to unfunctionalized reference capillaries (66%). Regarding carbodiimide activated immobilization, protease on unfunctionalized and aminated supports exhibited a significantly larger specific activity (0.99 μmol/min/mg) than enzymes on carboxylated surfaces (0.15 μmol/min/mg), which suggests preferred enzyme orientation. In protein hydrolysis, these differences in surface-enzyme interactions were reflected by variations in peptide composition and degree of hydrolysis. Accordingly, we demonstrate that surface functionalization critically determines the surface properties of protease support materials for the production of peptides under flow and allows tailoring the performance of proteolytic capillary membranes.journal articleBand:147119 102 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Amorphous arsenic sulfide nanoparticles in a shallow water hydrothermal system(Elsevier Science, 2019-04-23); ; ; ; Hydrothermal fluids can contain trace elements such as arsenic (As), which are toxic to surrounding biota. In these kind of fluids, the bioavailability and biotransformation of As have been investigated but so far the ratio of total soluble As (<200 nm) versus the amount of As contained in a nanoparticulate phase has not been reported. Here, for the first time, the presence of As in the nanoparticulate fraction (between 200 and 20 nm) is described for arsenic-rich hydrothermal fluids in a marine shallow-water hydrothermal system. Samples of diffusively venting hydrothermal fluids, pore-water and seawater were collected in the hydrothermal system located in Paleochori Bay, Milos Island (Greece), and the fraction between 200 and 20 nm (As200-20) was studied. Up to 38% of the soluble arsenic was present within the As200-20 fraction in pore fluids, 10 to 20% in hydrothermal fluids and 5% in seawater. Identification and characterization of particles in hydrothermal fluid, pore-water and seawater was performed by scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) with selected area electron diffraction (SAED) and dynamic light scattering (DLS). The particles are of spherical morphology with a polydisperse size distribution (PDI: 0.37) and diameters close to 100 nm. EDX studies confirmed a chemical composition rich in As and S. The SAED pattern revealed absence of a crystal phase indicating the presence of an amorphous arsenic sulfide material. These results bring into discussion the role of the nanoparticulate fraction for As dispersion, bioavailability, and potentially harmful effects in marine coastal ecosystems.journal articleBand:211100 163 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Edible high internal phase Pickering emulsion with double-emulsion morphology(Elsevier {BV}, 2020-10-24); ; ; ; Food-grade high internal phase Pickering emulsions (HIPPEs) unify the stability of Pickering emulsions and the advantages of detergent-based high internal phase emulsions (HIPEs), making them attractive as nutritional products. However, as oral delivery systems, HIPPEs are usually prepared in the form of o/w emulsions, which are suitable mainly for oleophilic active ingredients and may suffer from leakage during gastric digestion. To better protect and deliver hydrophilic cargo molecules, we developed a HIPPE-based w/o/w double emulsion system. Zein nanoparticles and soybean lecithin are found to have a synergistic effect in stabilization — using both natural emulsifiers together results in the formation of w/o/w double emulsions with improved stability, which is further confirmed by the interfacial tension and rheology of zein- and/or lecithin-laden oil-water interfaces. A combination of zein nanoparticles and lecithin achieves the fastest interfacial tension decrease, indicating an improved interfacial activity. Besides, lecithin contributes to the strong surface elasticity of the interfacial films, which makes the formed emulsions even stabler. Simulated digestion experiments suggest that the inner aqueous droplets can be strongly protected from gastric fluids. This edible HIPPE with double emulsion morphology provides new ideas for designing healthy foods for nutrients delivery.journal articleBand:111113 213 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Hydrophobic ceramic capillary membranes for versatile virus filtration(Elsevier, 2018-10-23); ; ; ; In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardJess of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of - 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiXl 74. The functionalized membranes allow a high membrane flux of - 150 L/(m2hbar), with throughput rates up to - 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.journal articleBand:570-571120 172 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Mineralization of iron oxide by ferritin homopolymers immobilized on SiO2 nanoparticles(2018-10-25); ; ; ; The iron storage protein ferritin is well known for its ability to mineralize iron oxides in its interior cavity. In this study, the authors investigated the mineralization behavior of H and L ferritin homopolymers assembled from individual subunits. The authors’ approach included molecular dynamics simulations, which suggested that ferritin subunits arrange themselves on silica surfaces with the active side facing away from the interface, although non covalent adsorption interactions might be weak. In experimental studies, the nucleation of iron oxide nuclei could be observed at ferritin homopolymers which were covalently immobilized through the EDC/NHS strategy at the surface of silica nanoparticles. Mineralization was initiated by the addition of ammonium iron (II) sulfate hexahydrate ((NH4)2Fe(SO4)2·6H2O) as the source of iron ions and trimethylamine N-oxide as the oxidant. The results demonstrate that immobilized H and L ferritin homopolymers on silica surfaces are able to induce the formation of a cohesive thin film of magnetic iron oxide crystals (magnetite and/or maghemite).journal article94 77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Assessment of nanoparticle immersion depth at liquid interfaces from chemically equivalent macroscopic surfaces(Elsevier Science, 2022-04); ; ; ; Hypothesis: We test whether the wettability of nanoparticles (NPs) straddling at an air/water surface or oil/water interface can be extrapolated from sessile drop-derived macroscopic contact angles (mCAs) on planar substrates, assuming that both the nanoparticles and the macroscopic substrates are chemically equivalent and feature the same electrokinetic potential. Experiments: Pure silica (SiO2) and amino-terminated silica (APTES-SiO2) NPs are compared to macroscopic surfaces with extremely low roughness (root mean square [RMS] roughness ≤ 2 nm) or a roughness determined by a close-packed layer of NPs (RMS roughness ∼ 35 nm). Equivalence of the surface chemistry is assessed by comparing the electrokinetic potentials of the NPs via electrophoretic light scattering and of the macroscopic substrates via streaming current analysis. The wettability of the macroscopic substrates is obtained from advancing (ACAs) and receding contact angles (RCAs) and in situ synchrotron X-ray reflectivity (XRR) provided by the NP wettability at the liquid interfaces. Findings: Generally, the RCA on smooth surfaces provides a good estimate of NP wetting properties. However, mCAs alone cannot predict adsorption barriers that prevent NP segregation to the interface, as is the case with the pure SiO2 nanoparticles. This strategy greatly facilitates assessing the wetting properties of NPs for applications such as emulsion formulation, flotation, or water remediation.journal articleBand:61165 70 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Bifunctional submicron colloidosomes coassembled from fluorescent and superparamagnetic nanoparticles(Wiley-VCH Verlag GmbH & Co. KGaA, Weilheim, 2015-01-02); ; ; ; Colloidosomes are microcapsules consisting of nanoparticle shells. These microcarriers can be self-assembled from a wide range of colloidal particles with selective chemical, physical, and morphological properties and show promise for application in the field of theranostic nanomedicine. Previous studies have mainly focused on fairly large colloidosomes (>1 μm) based on a single kind of particle; however, the intrinsic building-block nature of this microcarrier has not been exploited so far for the introduction of tailored functionality at the nanoscale. We report a synthetic route based on interfacial shear rheology studies that allows the simultaneous incorporation of different nanoparticles with distinct physical properties, that is, superparamagnetic iron oxide and fluorescent silica nanoparticles, in a single submicron colloidosome. These tailor-made microcapsules can potentially be used in various biomedical applications, including magnetic hyperthermia, magnetic particle imaging, drug targeting, and bioimaging.journal article127 151 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Effect of divalent versus monovalent cations on the MS2 retention capacity of amino-functionalized ceramic filters(Royal Society of Chemistry, 2018-04-10); ; ; ; Ceramic capillary membranes conditioned for virus filtration via functionalization with n-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) are analyzed with respect to their virus retention capacity when using feed solutions based on monovalent and divalent salts (NaCl, MgCl2). The log reduction value (LRV) by operating in dead-end mode using the model bacteriophage MS2 with a diameter of 25 nm and an IEP of 3.9 is as high as 9.6 when using feeds containing MgCl2. In contrast, a lesser LRV of 6.4 is observed for feed solutions based on NaCl. The TPDA functionalized surface is simulated at the atomistic scale using explicit-solvent molecular dynamics in the presence of either Na+ or Mg2+ ions. Computational prediction of the binding free energy reveals that the Mg2+ ions remain preferentially adsorbed at the surface, whereas Na+ ions form a weakly bound dissolved ionic layer. The charge shielding between surface and amino groups by the adsorbed Mg2+ ions leads to an upright orientation of the TPDA molecules as opposed to a more tilted orientation in the presence of Na+ ions. The resulting better accessibility of the TPDA molecules is very likely responsible for the enhanced virus retention capacity using a feed solution with Mg2+ ions.journal articleBand:20Heft:16121 103