Sensors gravimetric

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 

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Liron, Z. Kaushansky, N. Frishman, G. Kaplan, D. Greenblatt, J., The polymer coated SAW sensor as a gravimetric sensor, Anal. Chem. 1997, 69, 2848 2854... 

Just as flexural waves can propagate at low speeds in a plate whose thickness is much less than the wavelength, a low-speed flexural wave can propagate in a cylindrical rod whose diameter is much smaller than the wavelength [87]. Because of the low wave speed, operation as a gravimetric sensor in liquids is possible, as with the flexural plate-wave sensor. The gravimetric sensitivity for this sensor is typically S = — l/(2p ), where a is the radius of the rod. 

Shifts of the resonance frequency of a quartz crystal microbalance in micro-gravimetric sensors (Richter et al. 2004b)... 

Metal films are, at first sight, obvious candidates for the application of the EQCM as a gravimetric sensor these materials are rigid, have relatively high relative atomic... 

The closely related process of corrosion is also amenable to study by the EQCM. Since the species transferred across the interface (metal ions) are generally relatively heavy, a gravimetric sensor is very sensitive. An excellent example of this... 

Table 10. Comparison of sensitivities and other characteristics of acoustic gravimetric sensors [228], 255], [256) international symbols (short form) have been used to denote specific cuts of the various materials...

Piezoelectricity. The Piezoelectric Ejfect. Because all acoustic gravimetric sensors are based on the phenomenon of piezoelectricity, it seems appropriate to discuss briefly the effect itself. Piezoelectricity was first observed by the Curie brothers (Jaques and Pierre) in 1880 [258]. It is a reversible phenomenon, consisting of linear electromechanical interactions between mechanical and electrical properties in certain crystals (Fig. 52). The effect is generated, as already men-... 

Chemical sensors can be of gas, liquid, and solid particulate sensors based on the phases of the analyte. Depending on the operating principle of transducer in a chemical sensor, it can be used as optical, electrochemical, thermometric, and gravimetric sensor. Chemical sensors also include a special branch referred to as biosensors for the recognition of biochemicals and bio-reactions. The use of biological elements such as organisms, enzymes, antibodies, tissues, and cells as receptors differentiates biosensors from conventional chemical sensors. 

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