|M.Sc Student||Tarnapolsky Ariela|
|Subject||Understanding QCM-D Response to Deposition and Attachment|
of Bacteria and Particles to Surfaces
|Department||Department of Chemical Engineering||Supervisor||Professor Viatcheslav Freger|
|Full Thesis text|
Quartz crystal microbalance with dissipation monitoring (QCM-D) is a powerful tool for studying adsorption and adhesion of molecules, polymers and nanoparticles by monitoring the change in frequency and dissipation of resonant oscillations of a solid substrate. However, its use for analyzing deposition of microparticles and living cells on surfaces has been hampered by the difficulties of interpretation. Here we report a new quantitative model of QCM-D response, presented as an equivalent mechanical impedance circuit. As an essential feature, we propose to model the particle interaction with surrounding fluid as a freely oscillating sphere, which is a valid approximation for microparticles. This reduces the number of fitting parameters and helps isolate those pertinent to the contact mechanics. We use the model to analyze deposition of different microparticles as well as Pseudomonas fluorescens bacteria on several substrates using QCM-D combined with real-time microscopy. The parameter space is increased by varying particle type and size, substrate surface chemistry and rigidity, and ionic strength of solution, which allows observing a wide spectrum of possible responses and transition from inertial to elastic loading, including rarely observed resonant regimes. Ultimately, we find that the model offers a reasonable quantitative description of the observed response for different microparticles and substrates, as well as for bacteria, and enables to extract physical characteristics of the contact in elastic and mixed loading regimes. It also reveals discrepancies between measured dynamic contact mechanics parameters and those anticipated from classical models. The new model can be a useful tool for interpreting and quantifying QCM-D data on adhesion of particles and living cells to surfaces, including time-dependent adhesion phenomena.