Comparative studies of Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance with Dissipation (QCM-D) for real-time identification of signaling pathway

Cell signaling is one of the fundamental processes that control the cell fate. It modulates the cell shape and mechanics. To identify the dynamic signaling pathway in situ, we need tools that are capable of monitor the real-time elasticity and viscosity changes as well as structural rearrangements. Atomic Force Microscopy (AFM) has been demonstrated to be an effective instrument to visualize membrane and cytoskeleton structures on live cells. It can also provide the mechanical stiffness information by recording force displacement curves. Meanwhile, the viscoelasticity change by signaling pathways can be measured as the change of dissipation of a monolayer of cells by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). In the current study, we use the human epidermoid carcinoma A431 cell line as a model system which will be stimulated by epidermal growth factor (EGF). AFM was first used to image the structure of live A431 cells before and after stimulation; force measurement was also performed to analyze the dynamic elasticity change. The change of viscoelasticity of the A431 cell induced by EGF was monitored in real time on a QCM-D in terms of dissipation change and frequency shift. The mechanical property measurements from AFM and QCM-D experiment was analyzed and compared. Quantitative analysis can be performed to obtain the dynamic modulus of the material through theoretical modeling. This novel combination can be complementary to each other. A unified profile can therefore be generated as an effective indicator of signaling pathways such as cell proliferation and apoptosis.