Quartz Crystal Microbalance for Bioanalytical Applications

Abstract

The quartz crystal microbalance (QCM) was first introduced as a mass sensor in gas phase and in vacuum. Since oscillator circuits capable of exciting shear vibrations of quartz resonators under liquid load have been developed, the QCM became accepted as a new powerful technique to monitor adsorption processes at solid/liquid interfaces in chemical and biological research rendering the method an attractive low-cost alternative for bioanalytic applications. In the last decade, adsorption of biomolecules on functionalized surfaces turned out to be one of the paramount applications of piezoelectric transducers comprising the interaction of DNA and RNA with complementary strands, specific recognition of protein-ligands by immobilized receptors, the detection of virus capsids, bacteria, mammalian cells and last but not least the development of complete immunosensors. Piezoelectric transducers allow a label-free detection of molecules; they are more than mere mass sensors since the sensor response is also influenced by interfacial phenomena, viscoelastic properties of the adhered biomaterial, surface charges of adsorbed molecules and surface roughness. These new insights have recently been used to investigate the adhesion of cells, liposomes and proteins onto surfaces allowing to determine morphological changes of cells as a response to pharmacological substances and changes in the water content of biopolymers in situ. However, future will show whether the quartz crystal microbalance will assert itself against established label-free sensor devices like surface plasmon resonance spectroscopy and interferometry.