Quartz crystal microbalance , piezoelectric sensor

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

Piezoelectric mass deposition sensor (quartz crystal microbalance)... 

Mass sensors measure the change in mass upon interaction with the analyte. There are two main types of mass sensors quartz crystal microbalance (QCM) and surface acoustic wave (SAW). QCM measures the mass per unit area by measuring the change in frequency of a quartz crystal resonator. SAW uses a piezoelectric sensor to convert an electric signal into a mechanical wave that is then reconverted into an electric signal. Changes in amplitude, phase, frequency, or time delay between the input and output electrical signals are used to measure the concentration of the analyte. 

S.J. LASKY and D.A. BUTTRY, "Sensors Based on Biomolecules Immobilized on the Piezoelectric Quartz Crystal Microbalance", ACS Symp. Ser. 403 (1989) 183. 

This is the correct name for most popular mass sensors, although they are better known as Quartz Crystal Microbalances (QCMs). A piezoelectric crystal vibrating in its resonance mode is a harmonic oscillator. For microgravimetric applications, it is necessary to develop quantitative relationships between the relative shift of the resonant frequency and the added mass. In the following derivation, the added mass is treated as added thickness of the oscillator, which makes the derivation more intuitively accessible. 

Most cascade impactors do not give data in real time. The collection surfaces must be removed from the device and subjected to chemical or gravimetric analysis. However, one impactor does give data in real time. The Model PC-2 Air Particle Analyzer (California Measurements, Inc., Sierra Madre, CA) achieves a real-time measurement by using piezoelectric quartz crystal microbalance (QCM) mass sensors to electronically weigh particles at each impactor stage [62,63], The device has 10 stages and separates the aerosol into... 

The quartz crystal microbalance device (QCM)21-24 allows one to measure the change of the mass of the films. This method is based on the ability of a piezoelectric quartz crystal to oscillate at a resonance frequency determined by the mass of the crystal. For these measurements, gold is evaporated directly onto the surface of such a quartz sensor which is then exposed to the vapour or solution of the adsorbate. What makes this method very valuable is that it can be used like SPR for monitoring molecular adsorption/desorption at the surfaces in situ. 

The book is intended to give a state-of-the-art overview of the recent achievements in the area of piezoelectric sensors. The focus lies on TSM resonators, since this class of piezoelectric devices is most frequently used in physical and chemical sensor and biosensor apphcations, and they are largely commercially available. The book is divided into three parts. The first four chapters cover the physical background of piezoelectric devices. While Ralf Lucklum and Frank Eichelbaum discuss different interface circuits to drive a TSM resonator in the first chapter, Diethelm Johannsmann provides a comprehensive picture of how to treat different load situations of the quartz crystal microbalance (QCM) in the second, including rather new development in the area of con-... 

QCM can be described as a thickness-shear mode resonator, since weight change is measured on the base of the resonance frequency change. The acoustic wave propagates in a direction perpendicular to the crystal surface. The quartz crystal plate has to be cut to a specific orientation with respect to the ciystal axis to attain this acoustic propagation properties. AT-cut crystals are typically used for piezoelectric crystal resonators[7]. The use of quartz crystal microbalances as chemical sensors has its origins in the work of Sauerbrey[8] and King [9] who... 

Quartz Crystal Microbalance (QCM) sensors detect changes in mass adsorption at an interface and may represent an alternative sensor technology for the study of biospecific interactions in real-time [78], The operating principle of these sensors is based on changes of frequency in acoustic shear waves in the substrate of the sensor. When the QCM system is used in piezoelectric detection mode, the resulting frequency will shift in direct proportion to molecular mass adsorbed at the surface of the sensor [79]. 

Most chemists and materials scientists are not aware that an alternative gravimetric technology has been available for decades that provides sensitivities at least 3 orders of magnitude lower than mechanical balances, using a piezoelectric sensor that is rugged, inexpensive, and operates at high frequencies relatively immune to vibrations the quartz crystal microbalance. The purpose of this chapter is to describe the capabilities and limitations of the quartz crystal microbalance and to discuss its uses in thermal analysis and calorimetry. 

The response of piezoelectric devices propagating shear horizontal acoustic plate modes (SH-APMs) has been modeled and experimentally characterized for variations in surface mass, liquid rheological properties, and solution dielectric coefficient and electrical conductivity. The nature of the SH-APM and its propagation characteristics are outlined and used to describe a range of Interactions at the solid/liquid interface. Sensitivity to sub-monolayer mass changes is demonstrated and a Cu sensor is described. The APM device is compared to the surface acoustic wave device and the quartz crystal microbalance for liquid sensing applications. 

Sensors Based on Biomolecules Immobilized on the Piezoelectric Quartz Crystal Microbalance... 

Electrochemical quartz crystal microbalance (EQCM) or nanobalance (EQCN) is a combination of a piezoelectric sensor, i.e., a quartz crystal nanobalance (QCN) and an electrochemical cell containing the sample electrolyte solution, the reference electrode, as well as other electrodes as required, driving oscillator, amplifiers, and readout units [1-7]. In most electrochemical experiments, the piezoelectric crystal. 

The conductivity of the polymer layer may also depend on the physical state of the polymer. For instance, the sorption of organic vapors (e.g., alcohol) [130, 144,151,156] or acetone [154] causes a swelling of the polymer that alters the rate of interchain electron hopping. The mass change caused by the sorption can be followed by a piezoelectric quartz-crystal microbalance (QCM) or by sitrface acoustic wave (SAW) sensors. Optical changes can also be detected, although this effect is less frequently utihzed in gas sensors. 

Piezoelectric-based or acoustic wave (AW) sensors such as surface acoustic wave (SAW), quartz crystal microbalance (QCM) or bulk acoustic wave (BAW), and cantilever-based devices create a specific class of gas sensors widely used in various applications (Ippolito et al. 2009 Korotcenkov 2011) (see Fig. 13.1). Virtually all acoustic wave-based devices use a piezoelectric material to generate the acoustic wave which propagates along the surface in SAW devices or throughout the bulk of the structure in BAW devices. Piezoelectricity involves the ability of certain crystals to couple mechanical strain to electrical polarization and will only occur in crystals that lack a center of inversion symmetry (Ballantine et al. 1996). 

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