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@PHDTHESIS{Desio:836724,
      author       = {Desio, Silvia},
      title        = {{S}tatic and {D}ynamic {P}roperties of {B}io-{M}imetic
                      {S}ystems},
      school       = {HHU Düsseldorf},
      type         = {Dr.},
      reportid     = {FZJ-2017-05783},
      pages        = {104 p},
      year         = {2017},
      note         = {HHU Düsseldorf, Diss., 2017},
      abstract     = {We used total internal reflection microscopy (TIRM) to
                      measure the static interaction between colloidal probe
                      spheres and a flat glass wall. The technique was applied to
                      two fundamentally different systems. (i) The colloidal probe
                      spheres and/or the glass wall were covered with a so called
                      S-layer protein, Sgs-EGFP. In this case the protein-protein
                      interaction was investigated. (ii) Bare colloidal spheres
                      were suspended in a solution of rod shaped fd-virus next to
                      a bare glass wall. Here we were mainly interested in the
                      depletion interaction between the sphere and the wall
                      induced by the rods. In the latter case we also analyzed the
                      dynamic information, which is inherent to TIRM raw data, to
                      obtain further insight into the mechanism underlying the
                      sphere-wall interaction.Protein-protein interactions:
                      Measurements at increasing electrolyte content of the
                      suspending buffer showed that the sphere is stable against
                      irreversible sticking to the surface due to van der Waals
                      attraction at significantly higher ionic strength, if the
                      sphere and the surface are protein coated, as compared to
                      the case of bare surfaces. Qualitative data analysis implies
                      that there is an additional repulsive interaction on top of
                      the DLVO potential, which is effective over a range of tens
                      of nano-meters. This is at least one order of magnitude
                      larger than the range of so-called hydration forces, which
                      are usually considered responsible for protein stability
                      beyond DLVO-interaction.Depletion interaction induced by
                      fd-virus: We measured depletion potentials by TIRM over a
                      wide range of probe spheres sizes and rod concentrations to
                      explore the limits of the fundamental approximations used in
                      the classical Asakura-Oosawa theory (AO), which are the
                      treatment of the depletant as an ideal gas and Derjaguin
                      approximation, demanding that the sphere radius is much
                      larger than the rod length. The experimental data follow the
                      AO predictions at concentrations and size ratios, at which
                      this is expected to fail. At even higher fd-concentrations,
                      we observe deviations from the ideal gas behavior, which are
                      much larger and of opposite sign than predicted earlier. By
                      analyzing the dynamic information inherent to the raw data,
                      we found evidence that this observation is caused by the
                      dynamics of the rod network which is inevitably formed at
                      fd-concentrations above the overlap density. In a first
                      step, we used the initial slope of the intensity correlation
                      functions to determine spatially averaged particle diffusion
                      coefficients, which show a dependence on the
                      fd-concentration which is intriguingly similar to the
                      concentration dependence of the amplitude of the depletion
                      potential. Therefore, we assume that the large amplitude of
                      the apparent attractive potential at high fd-concentrations
                      is not anymore due to depletion forces but rather to the
                      particle being mechanically trapped in the network of
                      rods.To gain further insight into the systems dynamics, we
                      determined spatially resolved dynamic data. We found that
                      the particle’s drift velocity due to the external force
                      field can be determined with excellent accuracy, while it
                      appears to be generally much more difficult to measure
                      near-wall diffusion coefficients by TIRM. This finding might
                      open a new route to use TIRM as tool to measure local
                      viscosities at extremely low shear rates by a passive
                      micro-rheology approach.},
      cin          = {ICS-3},
      cid          = {I:(DE-Juel1)ICS-3-20110106},
      pnm          = {551 - Functional Macromolecules and Complexes (POF3-551) /
                      SOMATAI - Soft Matter at Aqueous Interfaces (316866)},
      pid          = {G:(DE-HGF)POF3-551 / G:(EU-Grant)316866},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/836724},
}