Abstract
We developed an impedance quartz crystal microbalance (QCM) approach with the ability to simultaneously record mass changes and calibrated energy dissipation with high sensitivity using an impedance analyzer. This impedance QCM measures frequency shifts and resistance changes of sensing quartz crystals very stable, accurately, and calibrated, thus yielding quantitative information on mass changes and dissipation. Resistance changes below 0.3 Ω were measured with corresponding dissipation values of 0.01 µU (micro dissipation units). The broadband impedance capabilities allow measurements between 20 Hz and 120 MHz including higher harmonic modes of up to 11th order for a 10 MHz fundamental resonance frequency quartz crystal. We demonstrate the adsorbed mass, calibrated resistance, and quantitative dissipation measurements on two biological systems including the high affinity based avidin-biotin interaction and nano-assemblies of polyelectrolyte layers. The binding affinity of a protein-antibody interaction was determined. The impedance QCM is a versatile and simple method for accurate and calibrated resistance and dissipation measurements with broadband measurement capabilities for higher harmonics measurements.
Highlights
Quartz crystal microbalance (QCM) is an acoustic sensing technique which uses the inverse piezoelectric effect for measuring different properties of surrounding media, such as mass adsorption or fluid viscosity
The first step of the biochemical reaction was to inject NeutrAvidin into the liquid cell leading to adsorption to the gold surface with a corresponding frequency shift of 240 Hz
In the second step biotinylated goat IgG-antibody was injected that binds to the NeutrAvidin layer via biotin resulting in frequency shift of 195 Hz
Summary
Quartz crystal microbalance (QCM) is an acoustic sensing technique which uses the inverse piezoelectric effect for measuring different properties of surrounding media, such as mass adsorption or fluid viscosity. Biochemical functionalization of the quartz crystal electrode allows a label-free detection of specific molecular interactions with high sensitivity and specificity and a real-time determination of kinetic rates and affinity constants This makes QCM a versatile bioanalytic screening tool for various applications ranging from the detection of single molecular monolayers, polymer films, complex macromolecules, to whole cells [5,6,7]. Dissipation serves as an additional parameter characterizing the deposited mass layer This additional information is critical for many biomolecular systems, including the investigation of conformational effects of ligand binding to a DNA complex [10], DNA hybridization, and DNA–protein interactions [11,12], or protein adsorption to biomaterials [13,14,15,16]
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