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    Dissipation in Films of Adsorbed Nanospheres Studied by Quartz Crystal Microbalance (QCM)

    Year: 2009

    Journal: Anal. Chem. 2009, 81, 8167–8176, 20100827

    Authors: Johannsmann D., Reviakine I., Richter R.P.

    Last authors: Ralf P. Richter

    Organizations: Institute of Physical Chemistry, Clausthal University of Technology, D-38678 Clausthal-Zellerfeld, Germany Biosurfaces Unit, CIC biomaGUNE, 20009 Donostia, San Sebastian, Spain Department of Biochemistry and Molecular Biology, University of the Basque Country, 48940 Leioa, Spain, and Department of New Materials and Biosystems, Max Planck Institute for Metals Research, D-70569 Stuttgart, Germany

    Country: Germany

    The quartz crystal microbalance (QCM) has become a popular method to study the formation of surface-confined films that consist of discrete biomolecular objects such as proteins, phospholipid vesicles, virus particlessin liquids. The quantitative interpretation of QCM datas frequency and bandwidth (or, equivalently, dissipation) shiftssobtained with such films is limited by the lack of understanding of the energy dissipation mechanisms that operate in these films as they are sheared at megahertz frequencies during the QCM experiment. Here, we investigate dissipation mechanisms in such films experimentally and by finite-element method (FEM) calculations. Experimentally, we study the adsorption of globular proteins and virus particles to surfaces with various attachment geometries: direct adsorption to the surface, attachment via multiple anchors, or attachment via a single anchor. We find that the extent of dissipation caused by the film and the evolution of dissipation as a function of surface coverage is not dependent on the internal properties of these particles but rather on the geometry of their attachment to the surface. FEM calculations reproduce the experimentally observed behavior of the dissipation. In particular, a transient maximum in dissipation that is observed experimentally is reproduced by the FEM calculations, provided that the contact zone between the sphere and the surface is narrow and sufficiently soft. Both a small-angle rotation of the sphere in the flow field of the background fluid (rocking) and a small-amplitude slippage (sliding) contribute to the dissipation. At high coverage, lateral hydrodynamic interactions between neighboring spheres counteract these modes of dissipation, which results in a maximum in dissipation at intermediate adsorption times. These results highlight that, in many scenarios of biomolecular adsorption, the dissipation is not primarily determined by the adsorbate itself, but rather by the link by which it is bound to the substrate.