User:Gabenwi/QCM-D

QCM-D
The Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) technique is a method for measuring changes occuring on surfaces,. The technique is useful for studying molecular interactions with surfaces as well as interactions between molecules. The technique is commonly used in the fields of biomaterials, energy, drug discovery, materials science and biophysics as well as in studying lipids, polymers and nanoparticle interactions. QCM-D is also used in studies of cell adhesion, spreading and growth.

Application areas include e.g. molecular adsorption/desorption and binding kinetics to various types of surfaces. Other typical applications are characterizing viscoelastic films, conformational changes of deposited macromolecules, build-up of polyelectrolyte multilayers, and degradation or corrosion of films and coatings.

QCM-D is a real-time, label-free, surface-sensitive technique. In addition to mass and thickness of the molecular layer or film coupled to the sensor surface QCM-D also gives information about the structural properties of the film. This technique is extremely sensitive and can normally measure about 0.5 ng/cm2.

In addition to adsorption/desorption processes, QCM-D also provides information about conformational changes, such as cross-linking, swelling/collapse of films or protein conformational changes. QCM-D is sensitive to the properties of the adsorbed molecules and the solvent that is coupled to or trapped between and around those molecules.

By combining QCM-D measurements with measurements from an optical technique such as surface plasmon resonance (SPR), dual polar interferometry (DPI) or ellipsometry that measures the optical mass (dry mass) of the molecular layer (i.e. the associated solvent is not detected), it is possible to extract information about the solvent content of the film.

The active component in the QCM-D technique is a thin quartz crystal disk sandwiched between a pair of electrodes. The application of an AC voltage over the electrodes causes the crystal to oscillate at its resonance frequency due to piezoelectricity. When the AC voltage is turned off, the oscillation decays exponentially. With the QCM-D technology, this decay is recorded and can be measured on the millisecond time-scale. The resonance frequency (f) and the energy dissipation factor (D) are extracted. D is defined as the loss of energy per oscillation period in relation to the total energy stored in the system.

Changes in the resonance frequency (Δf) are primarily related to mass uptake or release at the sensor surface. Changes in the dissipation factor (ΔD) are primarily related to the viscoelasticity (softness) and structural changes of the film adhering at the sensor surface. Current QCM-D equipment enables measuring of more than 200 data points per second thus allowing a high time resolution and a good signal-to-noise ratio of the monitored parameters.