Fig. 5

Schematic illustration (not to scale) of the two-layer-viscoelastic model suggested as a simplified representation of QCM-D responses in cell experiments. The interfacial layer between the cell and the sensor surface (index ‘1’) represents the structures responsible for the cell adhesion to the sensor surface, including the sensor coating, any material present between the sensor coating and the cell, the cell membrane, and material inside the cell associated with the cell membrane (shown inupper insert). The top layer (index ‘2’) approximates the bulk properties of the cell. H denotes maximal cell thickness estimated at ~10 μm, h the thickness of the interfacial layer and δ the penetration depth (sub-micrometer)