On the Use of the Quartz Crystal Microbalance for Whole-Cell-Based Biosensing

The quartz crystal microbalance (QCM) can be used and has often been used to study the interactions of cells with man-made surfaces. The instrument as such is simple. For screening purposes, one can easily run numerous resonators in parallel. The main problem is the interpretation of experimental data. Living cells by their very nature are enormously complicated and the limited amount of information obtained from a QCM experiment therefore is not easily turned into a meaningful diagnostic statement. In the first part, the text elaborates on the technical background with special emphasis on quantitative modeling. While thorough quantitative modeling is difficult, simplified models (which have a limited scope and which provide limited answers) can be applied. The text provides checks on consistency and applicability. These simple models are the Sauerbrey film (only applicable to biofilms on torsional resonators), the semi-infinite viscoelastic medium, and the coupled resonance. In search for more depth of information, one may explore novel sensing dimensions, which include the variation of amplitude, exploitation of piezoelectric stiffening, the analysis of temporal variations, and temperature sweeps. Given the instrument’s simplicity, one may combine the QCM with imaging techniques, with optical spectroscopy (even in transmission), and with electrical impedance spectroscopy. The situation is open. Probing whole cells and cell layers with a QCM is already a robust and reliable technique. A better understanding of data interpretation will expand the scope of possible applications.