Sensors BAW

BAW sensors are largely classic oscillating quartz crystals with metalUzed planes for contacting and are covered by acceptor layers selectively interacting with the analyte. The analyte is absorbed and causes a mass change in the oscillating system, which gives rise to frequency shift. The Sauerbrey equation (Sect. 2.1.3) is the basis of quantitative evaluation. 

Water vapor Gelatin lithium chloride polyethylene glycol 

Ammonia Pyridoxinhydrochloride Ascorbic acid + Silver nitrate 

Hydrogen sulfide Smolder residue of chlorbenzoic acid, (acetonic extract) silver acetate Hydrocarbons Non polar gas chromatographic separation phases, e.g. carbowax 550 

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Tan Y, Zhou Z, Wang P, Nie L, and Yao S. A study of a biomimetic recognition material for the BAW sensor by molecular imprinting and its application for the determination of paracetamol in the human serum and urine. Talanta 2001 55 337-347. 

Bulk acoustic wave (BAW) biosensors employ either longitudinal or shear waves, although the latter is often preferred to reduce acoustic radiation in the medium of interest. They are the oldest and the simplest acoustic wave devices. BAW devices consist of a parallel electrode placed on both sides of the thin piece of crystal. BAW sensor can technically employ any piezoelectric element, and typically quartz is used, as it is an inexpensive material readily available in nature and easily synthesizable in abundant quantities. In addition, thin disks of quartz are more stable at high temperatures than other piezoelectric elements. When an alternating electric field is applied, it results in a potential difference... 

Theory BAW sensors utilize quartz crystal as a substrate. Generally, the crystal is a thin disk where square or rectangular metal electrodes are deposited on the opposite faces. Frequency is changed according to mass change, which can be calculated by Eq. 9 under the assumption that the change in mass is negligible compared to the mass of the crystal Am m) ... 

Applications. This section will be limited to a brief consideration of the use of BAW sensors in gas-sensing devices and as sensors for liquid phases. Piezoelectric microbalances can also be used for monitoring such heterogeneous samples as aerosols and suspensions, as discussed in [262]. 

Table 14. Survey of selected reports on BAW sensors for inorganic and organic analytes [230]...

Selectivities of BAW sensors differ according to their acceptor layer. Whereas palladium is highly selective for hydrogen, organic amines are only weakly selective for sulphur dioxide, and carbowaxes (well known as stationary phase in chromatography) interact with numerous non-polar gases, hence they are non-selective sensors for hydrocarbons. Response time also varies within a wide range. 

In electrochemistry, the piezoelectric BAW sensor is known as an electrochemical quartz crystal microbalance (EQCM). This device plays an important role in electrochemical research. Metal deposition, corrosion and formation of passive layers have been studied successfully. 

In another application of MIPs, Peng et al. devised a biomimetic bulk acoustic wave (BAW) sensor based on ab MIP as a non-aqueous assay for phenobarbital. The MIP, which was based on phenobarbital template and methacrylic functional monomer, was prepared through a noncovalent method, and the resulting sensor was found to work selectively and sensitively in absolute ethanol (linearity range of the response was in the range of 9.0 X 10" M and 5.0 X 10" M and a detection limit of 5.0 x 10" M was observed [452]. 

QCM sensors (or BAW sensors) concern probing alterations to the bulk properties of the piezoelectric crystal. If an acoustic wave is made to travel along the surface of the substrate, then a surface acoustic wave (SAW) sensor can be produced. 

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