Bulk acoustic wave sensors

Alternatively the capillary rise can be measured using a bulk acoustic wave sensor [97Che]. (Data obtained with these methods are labelled BAW). 

Tan YG, Peng H, Liang CD, Yao SZ. A new assay system for phenacetin using biomimic bulk acoustic wave sensor with a molecularly imprinted polymer coating. Sens AcUiat B 2001 73 179-184. 

Any of the methods of detection used in liquid chromatography can be used in IC, though some are more useful than others. If the eluent does not affect the detector the need for a suppressor disappears. Common means of detection in IC are ultraviolet (UV) absorption, including indirect absorption electrochemical, especially amperometric and pulsed amperometric and postcolumn derivatization. Detectors atomic absorption spectrometry, chemiluminescence, fluorescence, atomic spectroscopic, refractive index, electrochemical (besides conductivity) including amperometric, coulometric, potentiometric, polaro-graphic, pulsed amperometric, inductively coupled plasma emission spectrometry, ion-selective electrode, inductively coupled plasma mass spectrometry, bulk acoustic wave sensor, and evaporative light-scattering detection. 

Pyrimethamine MAA, EGDMA Thermal, monolithic Bulk acoustic wave sensor... 

H. Peng, C. Liang, A. Zhou, Y. Zhang, Q. Xie and S. Yao, Development of a new atropine sulfate bulk acoustic wave sensor based on a molecularly imprinted electrosynthesized copolymer of anihne with 0-Phenylenediamine, A a/. Chim. Acta, 423 (2) 221-228,2000. 

H. Peng, C.D. Liang, D.L. He, L.H. Nie and S.Z. Yao, Bulk acoustic wave sensor using molecularly imprinted polymers as recognition elements for the determination of pyrimethamine, Talanta, 52 (3) 441-448, 2000. 

A schematic diagram of a bulk acoustic wave (BAW) chemical sensor is composed of a BAW piezoelectric resonator with one or both surfaces covered by a membrane (CIM) (fig. 14). 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

To model this, Duncan-Hewitt and Thompson [50] developed a four-layer model for a transverse-shear mode acoustic wave sensor with one face immersed in a liquid, comprised of a solid substrate (quartz/electrode) layer, an ordered surface-adjacent layer, a thin transition layer, and the bulk liquid layer. The ordered surface-adjacent layer was assumed to be more structured than the bulk, with a greater density and viscosity. For the transition layer, based on an expansion of the analysis of Tolstoi [3] and then Blake [12], the authors developed a model based on the nucleation of vacancies in the layer caused by shear stress in the liquid. The aim of this work was to explore the concept of graded surface and liquid properties, as well as their effect on observable boundary conditions. They calculated the hrst-order rate of deformation, as the product of the rate constant of densities and the concentration of vacancies in the liquid. 

MOS metal oxide sensor, MOSFET metal oxide semiconductor field-effect transistor, IR infrared, CP conducting polymer, QMS quartz crystal microbalance, IMS ion mobility spectrometry, BAW bulk acoustic wave, MS mass spectrometry, SAW siuface acoustic wave, REMPI-TOFMS resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry... 

Surface acoustic waves (SAW), which are sensitive to surface changes, are especially sensitive to mass loading and theoretically orders of magnitude more sensitive than bulk acoustic waves [43]. Adsorption of gas onto the device surface causes a perturbation in the propagation velocity of the surface acoustic wave, this effect can be used to observe very small changes in mass density of 10 g/cm (the film has to be deposited on a piezoelectric substrate). SAW device can be useful as sensors for vapour or solution species and as monitors for thin film properties such as diffusivity. They can be used for example as a mass sensor or microbalance to determine the adsorption isotherms of small thin film samples (only 0.2 cm of sample are required in the cell) [42]. 

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

The most commonly known oscillator sensors are bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices. The BAW devices operate according to the Sauerbrey principle that very thin films on AT-cut crystals can be treated as equivalent mass changes of the crystal. The SAW devices can operate either on the Rayleigh wave propagation principle at solid thin-film boundaries [3] or as bulk wave devices [4]. 

Functional polymers may be used for dihierent types of chemical sensors, including acoustic wave sensors (bulk acoustic wave, surface acoustic wave, and flexural plate wave sensors), electronic conductance sensors (semiconducting and capacitance sensors), and calorimetric sensors. ... 

Based on a thin-fllm bulk acoustic wave resonators (TFBAR) coated with tetraphenyl CoPP, an electroacoustic chemical sensor can detect ethanol vapor down... 

Piezoelectric bulk acoustic wave (BAW) chemical vapor sensor Glucose sensor... 

Among the different types of sensors, the most commercially used ones in e-nose systems include metal oxide semiconductors, conducting polymers, bulk acoustic waves, surface acoustic waves, quartz-microbalance sensors and tin oxide sensors. 

The goal of this entry is to categorize and describe the mainstream acoustic wave biosensors. We will begin by discussing biosensors that utilize bulk acoustic waves and subsequently analyze devices that employ surface acoustic waves. We will also examine sensors that employ... 

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... 

TSM resonators possess lower mass sensitivity than most acoustic wave sensors that employ other mechanisms since they typically operate between only 5 and 30 MHz. Thinner devices can be used to increase frequencies that result in increased mass sensitivity, and they are more fragile and harder to manufacture and handle [5]. Recent research on this topic has been on creating high-frequency TSM resonators with piezoelectric Aims and bulk silicon micromachining techniques. 

MEMS-Based Acoustic Wave Biosensors Introduction A MEMS-based acoustic wave biosensor is a chemical sensor which detects changes in resonant frequency of a mechanical resonator when biomolecules are adsorbed on the surface of a biologically active membrane. Since frequency change can be measured very precisely, very small mass changes can be measured. This leads to high sensitivity of the biosensors. Typical acoustic wave biosensors are bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensors. 

The key feature of all acoustic wave sensors for detecting vapors is that measurable characteristics of the acoustic wave is altered as a result of adsorption on the surface of a receptive layer or absorption into the bulk of a thin layer (Figure 3). After sorption of the vapor by a thin film on top of the acoustic resonator equilibrium conditions are established and as a consequence of the increased mass or more accurately the change in the phase velocity of the acoustic wave a signal is created. Surface coatings generally enhance the sorption of vapors with the key properties of selectivity and sensitivity while affording reversibility. Typically, rubbery polymers were used on SAW devices such as polyisobutylene or substituted polysiloxanes but also self-assembled... 

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