Quartz Crystal Microbalance with Dissipation Monitoring

Abstract

The quartz crystal microbalance with dissipation monitoring (QCM-D) is an ultrasensitive mechanical sensing device that is capable of providing real-time, non-invasive measurements of changes in resonance frequency and energy dissipation responses of cells immobilized onto the sensor surface. The majority of its applications in cell research have been limited to the study of the adhesive interaction between cells and the substrate surface and the evaluation of the effect of an external stimulant on the adhered cells. The overall objective of this thesis work was to further exploit the capabilities of the QCM-D in cell research by addressing important problems that are relevant to fundamental biology and medicine. In the project presented in Chapter 4, we examined the EGF-induced cell de-adhesion, a critical step in normal embryonic development, wound repair, inflammatory response, and tumor cell metastasis. We were able to successfully establish the change in the energy dissipation factor ([delta]D-response) as a specific and quantitative measure of cell adhesion. With this novel measure of cell adhesion, we characterized this complex de-adhesion process, which appeared to exhibit an initial rapid cell de-adhesion, a transition, and a slow re-adhesion. We also shed light on the dynamic coordination of the three downstream pathways of epidermal growth factor receptor (EGFR) signaling in mediation of the epidermal growth factor (EGF)-induced de-adhesion process. In chapter 5, continuing with the theme of applying this novel measure to the characterization of cell adhesion, we examined the adhesion process of human epidermal keratinocytes on the implant type of surface. We identified three distinct stages of this adhesion process and developed several new strategies for strengthening the adhesion between soft tissue/skin/bone and implants. In chapter 6, we extended this novel measure of cell adhesion to the investigation of GPCR signaling by capitalizing the regulatory role of G protein-coupled receptor (GPCR) signaling in mediation of cell adhesion. We were able to dissect the multiplicity of the ligand-induced GPCR signaling and obtain mechanistic insights into the promiscuous coupling of G[alpha]q, G[alpha]s, and G[alpha]i pathways as well as their dynamic coordination. In chapters 7 and 8, we explored the potential of cell-based QCM-D assay in detection of biomarkers. In chapter 7, we were able to relate the [delta]D-response with the cellular response mediated by the high-affinity EGFR, the subclass of EGFR that is more relevant to cancer development. Lastly in chapter 8, we demonstrated that this cell-based QCM-D assay has the sensitivity and specificity to detect some of the potential biomarkers of ovarian cancer. In conclusion, this thesis work has demonstrated that the QCM-D is a highly sensitive, label-free technique that has the capabilities to probe some of the most important cellular processes, such as cell adhesion and cell signaling and to serve as a sensing platform for biomarker detection.