Sensor piezoelectric

A single crystal face can also be exposed to a stationary or flowing liquid solution, and the antibody anti-IgG immobilized on this face using a thin film of polyacrylamide gel [252]. The variation in frequency is then nnonitored as a function of time, and falls each time a solution containing IgG is injected. 

In order to determine IgG, the A protein is immobilized on the quartz crystal instead of the antibody anti-IgG [253]. In the presence of IgG, the resonance frequency of the crystal drops because of the fixation of IgG on the A protein. If the antibody anti-IgG is also added then this frequency drops further, which demonstrates that not all the fixation sites of IgG are saturated. Finally, rinsing with an acidic solution (pH 3) dissociates the IgG from the A protein, which returns the piezoelectric biosensor to a state where it is ready for a fresh IgG determination. 

This method can also be applied for the detection of microorganisms. The immobilization of the antibody anti-Candida enables the measurement of the pathogenic microbe Candida albicans at concentrations between 10 to 5 x 10 cells/cm [254], 

Labelling an antibody or antigen with an enzyme is an EIA or ELISA technique (see 3.3.3.d). The presence of the enzyme ensures the consumption of substrate, or the generation of product, in a quantity large enough for detection by a transducer, hence the term enzymatic amplification. 

This method has been used te construct an immunological sensor for albumin using the antibody anti-HSA (human serum albumin). The 

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Figure 3.24 depicts a piezoelectric sensor consisting of two oscillator circuits a detector crystal oscillator and a reference crystal oscillator. The two are identical except for the fact that the reference oscillator is not coated with biological material and is intended to correct for temperature and humidity fluctuations, as well as other interfering effects. The two oscillator frequencies are fed to a mixer that provides the difference in frequency between the two crystals. In order to use the piezoelectric effect to detect a target dissolved substrate it should be reacted with a suitable biocatalyst immobilized on the crystal by entrapment (deposition from an acrylamide solution), cross-linking, irradiation or pre-coating. 

The rate of sampling with piezoelectric sensors is limited by their physical characteristics and present technology to the millisecond range for applications in the liquid phase. The technique is versatile in that it can be used in a variety of locations. The solid state electronics necessary to operate the piezoelectric sensor are easily miniaturized, and data can be recorded continuously or periodically. A small computer with a reasonable memory could easily record data over long times. There may be some problems in deep-sea locations, simply because of the complications in packaging the sensor for high-pressure environments, although this problem may be surmountable. 

Fig. 4.1 Schematics, modes of vibration, and acronyms of piezoelectric sensors discussed in this chapter (adapted from Grate et al., 1993)...

There are several types of materials that exhibit the piezoelectric effect. Because it is inexpensive, and because it has a relatively strong piezoelectric coefficient, quartz is the material of choice for most piezoelectric sensor applications. It has a hexagonal crystallographic structure, with no center of symmetry. Both the magnitude of the piezoelectric coefficient and the extent of its temperature dependence are affected by the orientation of the cut of the crystal with respect to the main crystallographic axes. The most popular AT-cut is shown in Fig. 4.2. 

Other, secondary effects skew the response of the piezoelectric sensor when it is used as a gas sensor. These can be described phenomenologically as the hydrostatic effect (p), the frictional effect (x), and the sorption effect (m) ... 

Both enantiomers of Chirasil-Val receptors have been applied to optical and piezoelectrical sensors [20]. In this chapter only the result of the optical transduction principle is presented. 

Researchers have been exploring a variety of ways in which piezoelectric sensors can be used to help solve such problems. For example, composite fabrics have been developed for use as seat covers in which piezoelectric fibers are embedded in a ground material. The fibers detect the position a person takes on the seat, the person s weight, and any changes the person makes while seated in the car. This information can be used to determine whether an airbag needs to be deployed and, if so, to what pressure it should be inflated. 

The nonlinearity and hysteresis have a profound influence on application of piezoelectric sensors and actuators, particularly in high precision devices. Details and additional references can be found in [4],... 

Oag, R.M., PI. King, C.J. Mellor, M.W. George, J. Ke and M. Poliakoff, Probing the Vapor-Liquid Phase Behaviors of Near-Critical and Supercritical Fluids Using a Shear Mode Piezoelectric Sensor, Analytical Chemistry, 75, 479-485 (2003). 

Milanko, O.A, Milinkovic, S.A. and Rajakovic, L.V. Evaluation of coating materials used on piezoelectric sensors for the detection of organophosphorus compounds in the vapour phase, Anal. Chim. Acta, 269, 289 (1992). 

There are several applications of ZnO that are due to its excellent piezoelectric properties [28,164]. Examples are surface-acoustic wave (SAW) devices and piezoelectric sensors [28,165-167]. Typically, SAW devices are used as band pass filters in the tele-communications industry, primarily in mobile phones and base stations. Emerging field for SAW devices are sensors in automotive applications (torque and pressure sensors), medical applications (chemical sensors), and other industrial applications (vapor, humidity, temperature, and mass sensors). Advantages of acoustic wave sensors are low costs, ruggedness, and a high sensitivity. Some sensors can even be interrogated wirelessly, i.e., such sensors do not require a power source. 

Piezoelectric Piezoelectric sensor 1 nL and up PicoRAPTR www.edcbiosystems.com www.beckman.com... 

Piezoelectric Sensor Suits Small Mold Applications, PM A, July/Aug. 2003. 

This complex subsequently reacts with other reagents in the solution to produce either an insoluble dimer product, which also adsorbs on the AW device surface, or a massive ion (l3 was used) that inserts into an ionic binding site in the surface film. Thus, the areal mass increase per bound analyte is significantly amplified. While these and other immunosensor detection schemes can involve rather complex reagent and/or buffer systems, the relative advantages of piezoelectric sensors in terms of cost, speed, and safety make them attractive alternatives to radioimmunoassay and other standard assay techniques. 

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