Why would you want to measure mass and thickness of thin films? One reason to monitor these two parameters is to characterize the build-up and degradation of molecular layers. Also, numerous materials and thin coatings are dynamic in nature and undergo physical changes responding to various stimuli, such as light, temperature, salt concentration or pH. These changes influence the mass, thickness and the structural properties of the material. The mass and thickness are therefore two parameters that are very much involved both the creation, behavior, and degradation of thin films. This makes them relevant to monitor both in the design, characterization, evaluation and optimization of thin films and coatings.
During surface interaction processes such as for example binding of molecules, adsorption, desorption, aggregation, and build-up of multilayer films, the mass and thickness of the molecular layers change. By measuring these changes in real time, we can follow the molecular binding processes and rearrangements. To measure these changes on a molecular scale, we need real-time nanoscale techniques. Once such technique is Quartz Crystal Microbalance with Dissipation monitoring technology (QCM-D). The QCM-D measures the changes of two parameters, the resonance frequency (f) and the energy dissipation (D). From these two parameters, mass and thickness changes at the surface can be extracted. In general, as the mass increases at the surface, the f will decrease. The D-parameter will indicate how soft the layer is. The softer the layer the higher the D. In the case of mass loss, the frequency will instead increase. And if the layer goes from soft to stiff, then the D parameter will decrease.
Molecules that are typically studied with this surface sensitive technology include lipids, proteins, DNA, polymers, surfactants, nanoparticles.
Let us take an example of a mass measurement. Here we are interested in detecting when an anti-biotin antibody first binds to a biotinylated lipid bilayer. We would also like to detect the cleavage of the antibody by an enzyme.
This measurement shows how monitoring of the mass changes allows us to detect both the binding of the antibody and the cleavage by the enzyme. Overall, the measurement offers insight in to both the molecular interaction processes and verifies the function of the enzyme as well as the direction of the antibody at the surface.
Figure 1. Mass changes as an antibody binds to the biotinylated bilayer on the surface (I-II) followed by enzyme cleavage (III) which removes 1/3 of the mass at the surface.
Download our overview to read more about what information you can extract from QCM-D analysis.
Read about what determines the sensing depth of the QCM-D technology and get examples of typical values
Register for the webinar
Read the guidelines on how to decide which QCM instrument will be the most suitable for your needs
Read about how protein adsorption at various surface and solution conditions quickly can be measured
Read about what single-harmonic and multi-harmonic QCM-D means and what the difference is between these instruments.
Read about how QSense QCM-D analysis is used as a powerful tool to investigate protein-lipid nanoparticles binding affinity
Learn about the difference between the theoretical QCM sensitivity and the sensitivity which is relevant in a measurement situation.
Read about the piezoelectric effect and how piezoelectricity arises
Learn more about QSense 4th generation QCM-D platform which provides a sharper tool in the scientist toolbox and simplifies data interpretation.
Learn about how biointerfaces and biomolecular interactions can be studied using QSense® QCM-D and what information these measurements offer.
Read about Prof. Jackman's experience using QCM-D to study surfactant-interaction with model membranes
Gabriel Ohlsson, Ph.D., is a former employee at Biolin Scientific where he initially held a position as an application scientist and later as a sales manager. Dr. Ohlsson did his Ph.D. in engineering physics and has spent a lot of time developing sensing technologies for soft matter material applications. One of his main tools during this research has been the QCM-D technology.