title: Acoustic sensing of the bacterium-substratum interface using QCM-D and the influence of extracellular polymeric substances.
abstract: It is commonly assumed that bacterial presence on a QCM sensor-surface is associated with a negative frequency shift according to conventional mass-loading theory. Here, we demonstrate that bacteria adhering to QCM sensor-surface may yield positive frequency shifts up to 1.9×10(-6) Hz per bacterium according to a coupled-oscillator theory. Furthermore, it is demonstrated that the excretion of extracellular polymeric substances (EPS) by adhering bacteria can change the frequency shift in the negative direction by 1.7×10(-6) Hz per bacterium, according to conventional mass-loading theory. The difference in frequency shifts between an EPS-producing and a non-EPS producing staphylococcal strain correlated with the excretion of 3×10(-14) g EPS per bacterium, representing only a few percent of the weight of a bacterium. Thus an adsorbed molecular mass as low as a few percent of the mass of an adhering bacterium significantly alters the QCM-signal. Since adhesion of many different bacterial strains is accompanied by molecular adsorption of EPS, with potentially opposite effects on the QCM-signal, a combination of the coupled-oscillator and normal mass-loading theory has to be applied for proper interpretation of QCM-frequency shifts in bacterial detection.
authors.affiliation: Department of Biomedical Engineering, University Medical Center Groningen, University of Groningen, P.O. Box 196, 9700 AD Groningen, The Netherlands.
authors.forename: Adam L J
authors.initials: AL
authors.lastname: Olsson
authors.forename: Henny C
authors.initials: HC
authors.lastname: van der Mei
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Busscher
authors.forename: Prashant K
authors.initials: PK
authors.lastname: Sharma
mesh_terms: D001419:Bacteria; D001422:Bacterial Adhesion; D011108:Polymers; D058525:Quartz Crystal Microbalance Techniques / Q000592:standards*
chemical_list: D011108:Polymers