At first glance, Surface Plasmon Resonance (SPR) and Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) appear quite similar. Both technologies are used in surface interaction analysis, monitoring specific interactions, molecular binding, and adsorption events. While they share many similarities, significant differences exist in their experimental capabilities and information extraction. In this post, we clarify the key differences and provide examples of when to use each method.
Comparing two instruments of the respective technology, you will see a set of differences. Some of which are inherent in the measurement principle, and some which originate in the hardware design. Before deciding which method to use, you must, therefore, define which information output you are looking for and what the needed experimental capabilities to run the experiments are. Is the technology able to deliver the answers you seek, and is the supplier of the technology offering all the features that you need to run the experiments?
Starting with the respective technology and measurement principle, QCM (including the extended versions, QCM-D, QCM-I, QCM-A, etc) is an acoustic technology and SPR an optical one, Table 1. In brief, and without going into detail how the respective technology works, QCM measures resonance frequency changes, f, of an oscillating quartz crystal, while SPR measures changes of the surface plasmon resonance angle, ϴ. The resonance frequency of the crystal oscillation is sensitive to mass changes, and the SPR angle is sensitive to refractive index changes. In addition to f and ϴ, additional parameters may be captured by the respective technology, which then expands the amount of information that the technology can extract.
Table 1. Comparison between the parameters measured by QSense QCM-D and SPR technology.
Depending on which, and how many, captured parameters that are offered by the specific QCM supplier, information output from QCM technology ranges from mere qualitative information about time-resolved mass changes at the surface to quantitative information about mass, thickness, and viscoelastic properties at high time resolution. Conversely, information output offered by a standard SPR instrument ranges from relative information about refractive index changes at/ near the surface, to quantitative information about the refractive index, thickness, density, and surface coverage.
QCM-D and SPR are two surface-sensitive, real-time technologies with overlapping application areas that may initially appear similar. While they share some similarities, their differences can be critical depending on the scientific question or experimental needs. Both are valuable tools in surface interaction analysis, each offering unique strengths. QCM-D excels in providing detailed information on mass and viscoelastic properties, including the detection of dynamically coupled water, which is crucial for understanding the hydration and structural characteristics of, for example, biomolecular layers. Conversely, SPR is superior for analyzing binding kinetics and affinity, as well as detecting changes in the refractive index, making it essential for monitoring molecular interactions. Understanding these differences will help you choose the right technology for your specific experimental needs.
Download the overview to read more about the key differences between QCM-D and SPR, and to get examples of when to use which technology.
Malin graduated in engineering physics in 2006, where her research focused on the QCM-D technology. Since then, she has been scrutinizing the how’s and why’s of the world in general, and the world of QCM-D in particular.
