Quartz Crystal Microbalance (QCM) and Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) instruments are used to measure changes in mass on a quartz crystal sensor’s surface (Figure 1) in real-time. Since the 1960s, QCM has been used for precise monitoring of thin films and surface interactions for thin film deposition monitoring, surface science studies, biosensing, electrochemistry, polymer analysis, environmental monitoring, drug discovery, and food science.

Topics below:

• How are quartz crystals used in QCM technology?
• What is the piezoelectric effect?
• How does QCM work? Piezoelectricity and quartz crystal sensors
• What is the dissipation factor?
• What is QCM-D and how does it work?
• What is the difference between QCM and QCM-D?
• What is the significance of frequency and dissipation measurements?
• How accurate are QCM-D measurements?
• What are the key applications of QCM-D?
• What materials can be analyzed with QCM-D?

How are quartz crystals used in QCM technology?

Quartz crystal is a piezoelectric material that generates an electric charge in response to mechanical stress, and vice versa. QCM technology utilizes this property to precisely measure small changes in mass or thickness of layers adhering to the surface of a quartz crystal. QCM technology is built around a quartz disc, which is made to vibrate at a specific frequency by applying a suitable voltage. The resonant frequency of a quartz crystal changes in proportion to the mass deposited on its surface, allowing for precise measurement of extremely small mass changes.  In this way a quartz crystal acts as a highly sensitive mass sensor.

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What is the piezoelectric effect?

The piezoelectric effect is a property of materials (like quartz) to generate an electric charge in response to applied mechanical stress. A unique characteristic of the piezoelectric effect is that it is reversible, meaning that materials exhibiting the direct piezoelectric effect (the generation of electricity when stress is applied) also exhibit the inverse piezoelectric effect (the generation of stress when an electric field is applied).

How does QCM work? Piezoelectricity and quartz crystal sensors

QCM is based on the inverse piezoelectric effect, where a shift in the resonance frequency of a quartz crystal is used for measuring shifts in mass of the crystal and any surface film. QCM devices consist of a thin plate of single-crystal quartz with electrodes attached to each side of the plate. Because of the piezoelectric properties of quartz, the crystals can generate an electric potential when pressure is applied to the crystal surfaces.

When any material or molecule sits on top of the quartz sensor, there are changes in the mass on the surface that can be quantified by the QCM device in the form of changes in frequency. The QCM quantifies the mass variation by measuring the change in the resonant frequency of the quartz crystal. The QCM resonance frequency depends on the thickness of the quartz crystal sensor. QCM devices are highly sensitive and can measure differences in mass per unit area from nanograms to micrograms.

What is the dissipation factor?

The dissipation factor in QCM technology refers to a measurement of energy loss within the system during each oscillation cycle. This depicts how much energy is dissipated as heat within a layer adsorbed on a quartz crystal sensor surface. Dissipation measurements offer insight into the viscoelastic properties of the material layer attached to the sensor surface. The higher the dissipation factor, the softer or more viscoelastic material is on the surface; a lower value indicates a more rigid film.

What is QCM-D and how does it work?

QCM-D stands for Quartz Crystal Microbalance with Dissipation Monitoring. It operates by measuring changes in the resonance frequency and dissipative energy losses, also known as damping, of a quartz crystal resonator when mass is added or removed from its surface. When molecules or particles adsorb onto the crystal surface, the frequency decreases, and the amount of energy lost (dissipation) increases. These two measurements together provide insights into both the mass and viscoelastic properties of the material (Figure 2).

What is the difference between QCM and QCM-D?

QCM measures the change in frequency because of mass changes on the surface of a quartz crystal. QCM-D adds the measurement of dissipation, which reflects how energy is lost when the material adsorbs onto the crystal surface.

QCM-D is more powerful than QCM for studying soft, viscoelastic films or complex molecular interactions, as it provides more information on the material’s mechanical properties, such as rigidity or flexibility.

What is the significance of frequency and dissipation measurements?

The frequency shift (Δf) in QCM-D provides a measure of mass changes on the surface of the quartz crystal, following the Sauerbrey equation. The dissipation factor (ΔD) measures the energy lost as the oscillating crystal deforms, which is especially useful for studying soft or viscoelastic films. Together, these measurements give a fuller picture of the adsorbed layer’s properties, such as its thickness, density, and mechanical properties (rigidity or softness).

How accurate are QCM-D measurements?

QCM-D measurements are generally highly accurate and sensitive, capable of detecting mass changes on the order of nanograms per square centimeter. The accuracy can be influenced by factors such as temperature fluctuations, sensor quality, fluid properties, and surface roughness. To maximize accuracy, careful calibration, stable environmental conditions, and proper sensor handling are essential during experimentation.

What are the key applications of QCM-D?

QCM-D is used across a wide range of fields, including biophysics, surface science, and materials science. It’s often applied to study molecular interactions like protein-protein or protein-DNA binding, analyze thin films, monitor drug delivery systems, and evaluate surface coatings. In biomedical applications, it is particularly useful for studying cell adhesion, biofilm formation, and surface interactions with biological molecules.

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What materials can be analyzed with QCM-D?

QCM-D can be used to study a variety of materials, ranging from simple inorganic substances like metals and silica to complex organic and biological materials such as proteins, lipids, and polymers. The sensor surface can be functionalized with specific molecules to tailor the analysis to specific applications, enabling researchers to investigate everything from molecular interactions to coatings and thin film growth in real-time.

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3T Analytik develops innovative technological solutions for the monitoring of molecular binding and interactions and surface associated phenomena. Quartz Crystal Microbalance (QCM) and Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) technology is used to measure changes in mass on a quartz crystal sensor’s surface in real-time. The instruments from 3T ensure precise, easy surface analysis technology for established and emerging industrial and academic applications.