QCM-D
Encyclopedia
The Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) is a special type of QCM based on the ring-down technique,. The term QCM-D is a trademark owned by Q-sense AB, Gothenburg, Sweden. The active component of a QCM is a thin quartz crystal disk sandwiched between a pair of electrodes. The QCM-D differs from the conventional QCM by the principle of data acquisition, which is based on ring-down. The application of an AC voltage over the electrodes causes the crystal to oscillate at its acoustic resonance frequency. When the AC voltage is turned off, the oscillation decays exponentially. This decay is recorded and 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. D is equal to the resonance bandwidth divided by the resonance frequency. Other QCM instruments determine the bandwidth from the conductance spectra. Being a QCM, the QCM-D works in real-time, does not need labeling, and is surface-sensitive. Current QCM-D equipment enables measuring of more than 200 data points per second.
Changes in the resonance frequency (Δf) are primarily related to mass uptake or release at the sensor surface. When employed as a mass sensor, the instrument has a sensitivity of about 0.5 ng/cm2. Changes in the dissipation factor (ΔD) are primarily related to the viscoelasticity (softness). The softness, in turn, often is related to structural changes of the film adhering at the sensor surface.
When operated as a mass sensor, the QCM-D is often used to study molecular adsorption/desorption and binding kinetics to various types of surfaces. In contrast to optical techniques such as surface plasmon resonance
(SPR) spectroscopy, ellipsometry
, or dual polarisation interferometry
, the QCM determines the mass of the adsorbed film including trapped solvent. Comparison of the „acoustic thickness“ as determined with the QCM and the „optical thickness“ as determined by any of the optical techniques therefore allows to estimate the degree of swelling of the film in the ambient liquid.
Since the softness of the sample is affected by a large variety of parameters, the QCM-D is useful for studying molecular interactions with surfaces as well as interactions between molecules. The QCM-D is commonly used in the fields of biomaterials, cell adhesion, drug discovery, materials science, and biophysics. 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.
Changes in the resonance frequency (Δf) are primarily related to mass uptake or release at the sensor surface. When employed as a mass sensor, the instrument has a sensitivity of about 0.5 ng/cm2. Changes in the dissipation factor (ΔD) are primarily related to the viscoelasticity (softness). The softness, in turn, often is related to structural changes of the film adhering at the sensor surface.
When operated as a mass sensor, the QCM-D is often used to study molecular adsorption/desorption and binding kinetics to various types of surfaces. In contrast to optical techniques such as surface plasmon resonance
Surface plasmon resonance
The excitation of surface plasmons by light is denoted as a surface plasmon resonance for planar surfaces or localized surface plasmon resonance for nanometer-sized metallic structures....
(SPR) spectroscopy, ellipsometry
Ellipsometry
Ellipsometry is an optical technique for the investigation of the dielectric properties of thin films....
, or dual polarisation interferometry
Dual Polarisation Interferometry
Dual polarization interferometry is an analytical technique that can probe molecular scale layers adsorbed to the surface of a waveguide by using the evanescent wave of a laser beam confined to the waveguide...
, the QCM determines the mass of the adsorbed film including trapped solvent. Comparison of the „acoustic thickness“ as determined with the QCM and the „optical thickness“ as determined by any of the optical techniques therefore allows to estimate the degree of swelling of the film in the ambient liquid.
Since the softness of the sample is affected by a large variety of parameters, the QCM-D is useful for studying molecular interactions with surfaces as well as interactions between molecules. The QCM-D is commonly used in the fields of biomaterials, cell adhesion, drug discovery, materials science, and biophysics. 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.