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search.filters.applied.f.access: openAccess × Author: Kraus, Tobias × Start date: 2000 × DDC: 570 × Has files: Yes × Type: Text × WGL Institute: INM ×

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Now showing 1 - 4 of 4
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    Formation mechanism for stable hybrid clusters of proteins and nanoparticles
    (Washington D.C. : American Chemical Society, 2015) Moerz, Sebastian T.; Kraegeloh, Annette; Chanana, Munish; Kraus, Tobias
    Citrate-stabilized gold nanoparticles (AuNP) agglomerate in the presence of hemoglobin (Hb) at acidic pH. The extent of agglomeration strongly depends on the concentration ratio [Hb]/[AuNP]. Negligible agglomeration occurs at very low and very high [Hb]/[AuNP]. Full agglomeration and precipitation occur at [Hb]/[AuNP] corresponding to an Hb monolayer on the AuNP. Ratios above and below this value lead to the formation of an unexpected phase: stable, microscopic AuNP–Hb agglomerates. We investigated the kinetics of agglomeration with dynamic light scattering and the adsorption kinetics of Hb on planar gold with surface-acoustic wave-phase measurements. Comparing agglomeration and adsorption kinetics leads to an explanation of the complex behavior of this nanoparticle–protein mixture. Agglomeration is initiated either when Hb bridges AuNP or when the electrostatic repulsion between AuNP is neutralized by Hb. It is terminated when Hb has been depleted or when Hb forms multilayers on the agglomerates that stabilize microscopic clusters indefinitely.
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    Self-Healing Iron Oxide Polyelectrolyte Nanocomposites: Influence of Particle Agglomeration and Water on Mechanical Properties
    (Basel : MDPI, 2023) Oberhausen, Bastian; Plohl, Ajda; Niebuur, Bart-Jan; Diebels, Stefan; Jung, Anne; Kraus, Tobias; Kickelbick, Guido
    Self-healing nanocomposites can be generated by organic functionalization of inorganic nanoparticles and complementary functionalization of the polymer matrix, allowing reversible interactions between the two components. Here, we report on self-healing nanocomposites based on ionic interactions between anionic copolymers consisting of di(ethylene glycol) methyl ether methacrylate, sodium 4-(methacryloyloxy)butan-1-sulfonate, and cationically functionalized iron oxide nanoparticles. The materials exhibited hygroscopic behavior. At water contents < 6%, the shear modulus was reduced by up to 90%. The nanoparticle concentration was identified as a second factor strongly influencing the mechanical properties of the materials. Backscattered scanning electron microscopy and small-angle X-ray scattering measurements showed the formation of agglomerates in the size range of 100 nm to a few µm in diameter, independent of concentration, resulting in the disordering of the semi-crystalline ionic polymer blocks. These effects resulted in an increase in the shear modulus of the composite from 3.7 MPa to 5.6 MPa, 6.3 Mpa, and 7.5 MPa for 2, 10, and 20 wt% particles, respectively. Temperature-induced self-healing was possible for all composites investigated. However, only 36% of the maximum stress could be recovered in systems with a low nanoparticle content, whereas the original properties were largely restored (>85%) at higher particle contents.
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    Microgravity Removes Reaction Limits from Nonpolar Nanoparticle Agglomeration
    (Weinheim : Wiley-VCH, 2022) Pyttlik, Andrea; Kuttich, Björn; Kraus, Tobias
    Gravity can affect the agglomeration of nanoparticles by changing convection and sedimentation. The temperature-induced agglomeration of hexadecanethiol-capped gold nanoparticles in microgravity (µ g) is studied at the ZARM (Center of Applied Space Technology and Microgravity) drop tower and compared to their agglomeration on the ground (1 g). Nonpolar nanoparticles with a hydrodynamic diameter of 13 nm are dispersed in tetradecane, rapidly cooled from 70 to 10 °C to induce agglomeration, and observed by dynamic light scattering at a time resolution of 1 s. The mean hydrodynamic diameters of the agglomerates formed after 8 s in microgravity are 3 times (for low initial concentrations) to 5 times (at high initial concentrations) larger than on the ground. The observations are consistent with an agglomeration process that is closer to the reaction limit on thground and closer to the diffusion limit in microgravity.
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    Protein identity and environmental parameters determine the final physico-chemical properties of protein-coated metal nanoparticles
    (Washington D.C. : American Chemical Society, 2015) Dewald, Inna; Isakin, Olga; Schubert, Jonas; Kraus, Tobias; Chanana, Munish
    When a nanomaterial enters a biological system, proteins adsorb onto the particle surface and alter the surface properties of nanoparticles, causing drastic changes in physico-chemical properties such as hydrodynamic size, surface charge and aggregation state, thus giving a completely new and undefined physico-chemical identity to the nanoparticles. In the present work, we study the impact of the protein identity (molecular weight and isoelectric point) and the environmental conditions (pH and ionic strength) on the final physico-chemical properties of a model nanoparticle system, i.e. gold nanoparticles. Gold nanoparticles either form stable dispersions or agglomerate spontaneously when mixed with protein solutions, depending on the protein and the experimental conditions. Strikingly, the agglomerates redisperse to individually dispersed and colloidally stable nanoparticles, depending on the purification pH. The final protein coated nanoparticles exhibit specific stabilities and surface charges that depend on protein type and the conditions during its adsorption. By understanding the interactions of nanoparticles with proteins under controlled conditions, we can define the protein corona of the NPs and thus their physico-chemical properties in various media.