Quartz crystal microbalance detectors

Concentration (gravimetric, forward-scatter detectors, back-scatter detectors, J-attenuation detector, quartz crystal microbalance detector). 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

This detector is based on the collective oscillations of the free electron plasma at a metal surface. Typically a prism is coated with a metal film and the film coated with a chemically selective layer. The surface is illuminated by a laser and the amount of material adsorbed by the coating affects the angle of the deflected beam. This platform is theoretically similar in sensitivity to a quartz crystal microbalance. This is another platform whose selectivity is based on the coating. The typical coating is using bound antibodies thus, this device becomes a platform for immuno-sensors (12). 

Quartz crystal microbalance — The quartz crystal microbalance (QCM) or nanobalance (QCN) is a thickness-shear-mode acoustic wave mass-sensitive detector based on the effect of an attached foreign mass on the resonant frequency of an oscillating quartz crystal. The QCM responds to any interfacial mass change. The response of a QCM is also extremely sensitive to the mass (density) and viscoelastic changes at the solid-solution interface [i-vi]. 

Hydrogen chloride gas is a noxious byproduct of many industrial chloride processes, and a major product from the combustion of most solid-rocket boosters. A quartz crystal microbalance using trlphenylamine as coating with 10" g/frequency was reported (37). The detector was capable of detecting 10 g of or 2.5 x 10" molecules of HCl. The performance of the detector was demonstrated during the Titan-Centaur launch in 1975. 

Sorption and surface adsorption of chemical agents by a mat of polymer nanofibers can be detected gravimetrically using quartz crystal microbalance (QCM) detectors (Ding et al. 2004b, 2005c Kwoun et al. 2001). The mass sensor is essentially a circular quartz crystal with thin metal elecfiodes deposited on either side of it. The resonant frequency of the piezoelectric crystal in an AC field depends on the crystal characteristics as well as the mass of material deposited on its surface. The Sauerbrey equation predicts a linear relationship... 

MAS Ma, S.-L., Lu, Z.-W., Wu, Y.-T., and Zhang, Z.-B., Partitioning of dmg model compounds between poly(lactic acid)s and supercritical CO2 using quartz crystal microbalance as an in situ detector, J. Supercrit Fluids, 54, 129,2010. 

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