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    ABSTRACT: Magnetic bead cellulose (MBC) was prepared using sol-gel transition of viscose in the presence of maghemite (γ-Fe2O3) nanoparticles. The MBC particles were then activated with p-toluenesulfonyl chloride to yield tosyl-activated magnetic bead cellulose (MBC-Ts). The microspheres were characterized by light and electron microscopy, elemental analysis and atomic absorption spectroscopy to determine morphology, size, polydispersity and content of iron and tosyl groups. The functionality of the MBC-Ts microspheres was demonstrated using proximity ligation assay (PLA) to detect vascular endothelial growth factor in femtomolar concentration range. The MBC-Ts microspheres performed equally well as commercially available microparticles that are routinely used as solid support in solid phase PLA.
    Journal of Biotechnology 06/2013; · 3.18 Impact Factor
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    ABSTRACT: Dispersion based products have applications in every area of life. During formulation of new products the dispersion properties have to be adjusted to obtain the desired stability, textural and rheological properties. Most often stable colloidal dispersions are required, sometime however, weak flocculation is purposely induced to adjust structural properties. In other cases strong flocculation is helpful for dispersion separation. From this it is evident that classification of the state of a dispersion regarding flocculation (net attractive particle interaction) and quantification of its degree are necessary and routine tasks in every day formulation and optimization work. Zeta potential is commonly used to predict the stability of virtually all colloidal dispersions. This neglects that the Zeta potential concept is limited to classical electrostatically stabilized dispersions. It has to be emphasized, however, that nowadays new dispersion products are stabilized by different approaches (e.g. by steric or rheological stabilization). Sedimentation analysis by multisample analytical centrifugation with photometric detection is a rather simple but powerful and high throughput method to characterize the dispersed state/degree of particle interaction. Visualization of in situ separation behaviour allows for the classification and differentiation between the various instability phenomena such as swarm sedimentation (stable dispersion) and zone sedimentation (flocculation, agglomeration). Even more, complex systems with subfractions of particles exhibiting a different behaviour can also be analyzed. Sedimentation behaviour of different dispersions made from plain or decorated nanoparticles as a function of pH of the continuous phase is presented and analyzed in terms of the degree and type of flocculation and compared with predictions based on Zeta potential data. Results demonstrate that contrary to measured Zeta potential the colloidal stability of the dispersed particles and the degree of particle flocculation/agglomeration were always well predicted by the sedimentation behaviour.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2013; · 2.35 Impact Factor
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    ABSTRACT: Carefully designed colloidal properties are the prerequisite for successful diagnostic and therapeutic applications of magnetic fluids (MF). A high degree of dispersion (small particle size, absence of agglomeration) and stability is required. Multisample analytical centrifugation with high resolution photometric detection was applied to characterize the quality of a range of differently stabilized MF's. Comparison of the `fingerprints' gives a fast overview over differences in MF quality (quality of particle stabilization against aggregation, separation stability). Sedimentation kinetics and the distribution of sedimentation velocity allow for a more detailed quantitative comparison and ranking between different products and batches. Even without any material properties well dispersed samples with narrow distribution can be discriminated from samples with broader distribution and oversized particles (agglomeration).
    12/2010;

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