Abstract
A quartz crystal microbalance (QCM), modified to allow simultaneous resonant frequency ( f) and energy dissipation ( D) measurements, was used in aqueous solution to monitor the attachment and spreading of neutrophils on polystyrene and different pre-adsorbed plasma proteins on the QCM surface. A unique feature of this technique is that mass changes in the nanogram per cm 2 range can be sensed within short (∼μm) range of the surface. By measuring changes in the resonant frequency of the QCM, it can be used to detect the contact area of the cells with the substrate. The QCM technique used in this work also enables the measurement of the energy dissipation factor (the frictional and viscoelastic energy losses in the system) caused by cell attachment. These two parameters provide new information regarding the kinetics of the attachment and spreading of neutrophils. The QCM signals were monitored for neutrophils deposited on an uncoated polystyrene surface and on polystyrene surfaces pre-coated either with immunoglobulin G (IgG), human serum albumin (HSA) or fibrinogen (Fg). The decrease in resonant frequency for neutrophils deposited on the uncoated polystyrene and IgG-coated surfaces were considerably larger than for HSA- and Fg-coated surfaces, indicating a larger degree of cell spreading. The dissipation energy of the neutrophils deposited on IgG-coated surfaces is also considerably higher than for the other surfaces, indicating the involvement of Fc receptors in IgG-induced activation. Neutrophils deposited on HSA caused a markedly slower QCM response than the other surfaces. Furthermore, indications of degrading proteolytic enzymes secreted from neutrophils on the protein-coated surfaces were seen. This is an attractive instrumentation to monitor the adhesion process of cells in situ on a real time basis, without the interruption caused by fixation and staining necessary for different microscopic methods.
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