Quartz crystal microbalance with dissipation monitoring: enabling real-time characterization of biological materials and their interactions

Abstract

In recent years, there has been a rapid growth in the number of scientific reports in which the quartz crystal microbalance (QCM) technique has played a key role in elucidating various aspects of biological materials and their interactions. This article illustrates some key advances in the development of a special variation of this technique called quartz crystal microbalance with dissipation monitoring (QCM-D). The main feature and advantage of QCM-D, compared with the conventional QCM, is that it in addition to measuring changes in resonant frequency (Deltaf), a simultaneous parameter related to the energy loss or dissipation (DeltaD) of the system is also measured. Deltaf essentially measures changes in the mass attached to the sensor surface, while DeltaD measures properties related to the viscoelastic properties of the adlayer. Thus, QCM-D measures two totally independent properties of the adlayer. The focus of this review is an overview of the QCM-D technology and highlights of recent applications. Specifically, recent applications dealing with DNA, proteins, lipids, and cells will be detailed. This is not intended as a comprehensive review of all possible applications of the QCM-D technology, but rather a glimpse into a few highlighted application areas in the biomolecular field that were published in 2007.

FIGURE 1

Description of the main components in QCM-D. a: Typical QCM-D sensor with Au electrodes. b: Quartz crystal with alternating current applied across electrodes. c: Short circuiting the alternating current. d: The oscillatory decay as the quartz disk comes to rest. The frequency of the oscillating crystal, shown in b, is related to the total oscillating mass adsorbed on the surface, while the energy dissipation, shown in c, is related to the viscoelastic properties of the oscillating mass. Thus, changes in adsorbed mass of, for example, a rigid protein provide a change in frequency, but for viscoelastic masses such as biomacromolecules, there is a change both in frequency and dissipation.

FIGURE 2

Example of raw data from a QCM-D experiment. This particular example demonstrates the adsorption of human serum albumin (a) and an antibody for human serum albumin (c). Steps b and d correspond to buffer rinses. Frequency changes (Δf) are shown in blue on the left axis and dissipation changes (ΔD) are shown in red on the right axis. Note the frequency change of step a and lack of dissipation change indicating the rigid characteristics of the human serum albumin film as it adsorbs on the surface. In contrast, the adsorption of the antibody at c gives a large frequency and dissipation change, indicating both mass adsorbed and increased viscoelastic characteristics due to the incorporation of water. Also, the rinsing step at d shows how a conformational change of the antibody can be detected as the physisorbed antibody molecules are rinsed away. For more information see reference .