Publication Title: Theoretical Aspects of a Discrete-Binding Approach in Quartz-Crystal Microbalance Acoustic Biosensing
Journal: Physical Review Applied 11, 034031
Communication Type: Scientific Publication
By: Vasilios Raptis, Achilleas Tsortos, and Electra Gizeli
We present an elaboration of the discrete molecule binding theory in acoustic biosensing, as proposed by Tsortos (Biophys. J. 2008). Essentially, the parameters of a damped harmonic oscillator model are mapped to attributes of the sensor crystal and analyte molecules attached on it in the presence of water. This way, changes in wave frequency Δf and energy dissipation ΔD are linked with molecular properties, which can be evaluated by fitting the model to experimental data. The theory attempts to interpret measurements at low to medium levels of surface coverage where the film-formation assumption breaks down. The established linear relationship between the acoustic ratio ΔD/Δf and intrinsic viscosity [η], a structural hydrodynamic parameter of the analyte, is recovered. Moreover, possible semi-quantitative explanations are offered for the experimentally observed nonzero intercept and the plateau reached by ΔD/Δf when very short or very long molecular chains are measured. These incorporate various system parameters such as the character of the linker, the shape/size of the molecules, and the hydrodynamic interactions taking place at the sensor’s surface in solution. The presented model is formulated to hold for the quartz crystal microbalance (QCM-D) sensor and sheds new light in many standing questions regarding its operation with biological samples in liquid.