Biomaterials Tutorial

Quartz Crystal Microbalance

Jeanette Stein
University of Washington Engineered Biomaterials

Quartz crystal microbalance (QCM) is best described as an ultra-sensitive sensor able to measure small changes in mass on a quartz crystal resonator in real-time. Its measuring principle is based on impedance analysis of a piezoelectric quartz crystal (i.e., a crystal that is able to convert mechanical forces into an electrical impulse). The crystal is sandwiched between a pair of electrodes.  The electrodes are attached to an oscillator. An AC voltage is applied allowing the quartz crystal to oscillate at resonance.

The addition of either rigid or viscous layers onto one or both of the electrodes will produce changes in both frequency (f), and quality of resonance (Q factor) or signal dissipation. This information is normally obtained by modeling the impedance curve using an equivalent circuit model.

A QCM is about 100 times more sensitive than an electronic fine balance with a sensitivity of 0.1mg.  This extreme sensitivity means that a QCM is able to measure mass changes as small as a fraction of a monolayer or single layer of atoms.  The QCM crystals can be used in fluids or with visco-elastic deposits. So, the technique has proven useful to a number of biotechnological applications, including: ligand recognition by immobilized receptors, bacterial and protein adhesion, biofilm formation, viral and bacterial detection, DNA and RNA complementary strand recognition.

References:

1. What is a Quartz Crystal Microbalance? Oct. 2004. KSV Instruments Ltd.Onlinehttp://www.ksvltd.com/content/index/QCMZ500.
2. Cady WG. Piezoelectricity: An introduction to the theory and applications of electromechanical phenomena in crystal. New York, NY: McGraw-Hill Book Co. 1946.
3. Rickert J, Weiss T, Krass Q, Jung G, Göpel W. A new affinity biosensor: Self-assembled thiols as selective monolayer coatings of quartz crystal microbalances. Biosensors & Bioelectronics 1996; 11(6/7): 591-598.