Surface acoustic wave detector

The piezo-electric effect of deformations of quartz under alternating current (at a frequency in the order of 10 MHz) is used by coating the crystal with a selectively binding substance, e. g. an antibody. When exposed to the antigen, an antibody-antigen complex will be formed on the surface and shift the resonance frequency of the crystal proportionally to the mass increment which is, in turn, proportional to the antigen concentration. A similar approach is used with surface acoustic wave detectors [142] or with the surface plasmon resonance technology (BIAcore, Pharmacia). 

TABLE 53.3. Detection performance of arrayed surface acoustic wave detector - ChemSentry... 

The combination of chemical and biological sensors with flow injection has been demonstrated. Both more-traditional-type sensors such as pH electrodes and newer sensors such as fiber optics and surface acoustic wave detectors have been incorporated into FIA systems with success. An advantage that FIA brings to the sensor field is the possibility of turning a moderately selective sensor into a selective sensor by incorporating into the FIA system some type of selectivity enhancement technique such as gas diffusion, dialysis, and reactors. Finally the FIA systems permit renewable systems since sensor surfaces and reaction cells can be washed, surface regenerated, and reagents replenished on demand. 

Much of today s technology has been developed into commercially available detection equipment, however, and this equipment should allow first responders, whether they be police, fire, Hazmat, or EMS units, to detect the presence or absence of CWA. This equipment is available, reasonably priced, and will detect a wide array of chemical agents. The M9 paper and the M256 kit are simple and inexpensive devices that enable responders to rapidly detect classical CW agents. The photo-ionization detector, the ion mobility detector, the surface acoustic wave detector, and the colorimetric tubes give medical personnel an ability to deal with a wider array of chemicals. As a market evolves for these items of detection equipment, modifications for the civilian community will be made to simplify their usage and the costs associated with their acquisition and maintenance should decrease. 

Tables 4.3 and 4.4 list several substances that have been used to simulate the nerve agent GB and bhster agent HD, respectively, in detector testing. The listed chemicals in Table 4.3 are similar to GB in some aspects. For example, the structure of dimethyl methylphosphonate (DMMP) is very similar to that of GB. Both contain the CH3-P=0 group. The main difference between them is that the simulant does not have the more active fluoride (-F) function group, and thus, its toxicity is much lower than GB. Both compound molecules contain phosphorous. Therefore, it is possible to use DMMP as a simulant to evaluate the performance of a flame photometric detector, ion mobility detectors, or surface acoustic wave detector.

TABLE 60.2 Detection Performance of Arrayed Surface Acoustic Wave Detector ChemSentry... 

The methods and means for ecological diagnostics make rapid strides among all the NDT and TD developing areas. To provide the atmosphere monitoring recently the good results were achieved in the development of surface-acoustics wave sensors (SAW), laser measuring systems, infrared detectors and systems based on other physical principles. 

Joint Chemical Agent Detector (JCAD) This detector will employ surface acoustic wave technology to detect nerve and blister agents. It will also allow detection of new forms of nerve agents. 

The model immunoassay is the enzyme-linked immunosorbent assay (ELISA) in which a non-specific capture antibody is bound to a surface, such as a multi-well plate or small tube [13]. In the basic form of ELISA, a second antibody tagged with an enzyme interacts specifically with the analyte. The enzyme assay produces a colored product that is read with a spectrophotometer. There are many variations on the basic immunoassay format that serve to increase sensitivity, specificity, linear range, and speed. Many commercial instruments have been developed to take advantage of various technologies for reporter molecules. The immunoassay may be coupled to an electronic sensor and transducer, such as a surface acoustical wave (SAW) sensor. Electrochemiluminescence (ECL) is a method in which the detector antibody is tagged with a ruthenium-containing chelate [13-15]. When the tag is... 

Acoustic wave sensors are also used to detect nerve and blister agents. The surface acoustic wave chemical agent detector (SAW Mini-CAD) is a commercially available, pocket-sized instrument that can monitor for trace levels of toxic vapors of sulfur-based mustard agents (e.g., distilled mustard) and G nerve agents (e.g., tabun, sarin, soman) with a high degree of specificity. Colorimetric tubes are the... 

Microsensors have the potential for selective GC detectors and also as remote sensors when combined in arrays often referred to as electronic noses . Promising microsensors include surface acoustic wave (SAW) detectors normally coated with different semi-selective polymeric layers and microelectromechanical systems (MEMS) including microcantilever sensors. The hope is that, in the future, hundreds of such microcantilevers, coated with suitable coatings, may be able to achieve sufficient selectivity to provide a cost-effective platform for detecting explosives in the presence of potentially interfering compounds in real environments. This array of... 

Philippe Bergonzo and Richard B. Jackman, Diamond-Based Radiation and Photon Detectors Hiroshi Kawarada, Diamond Field Effect Transistors Using H-Terminated Surfaces Shinichi Shikata and Hideald Nakahata, Diamond Surface Acoustic Wave Device... 

Matsushita, K., Sekiguchi, H., Seto, Y. (2005). Performance of portable surface acoustic wave sensor array chemical agent detector. Bunseki Kagaku 54 83-8. 

Another state-of-the-art detection system contains a surface acoustic wave (SAW) device, which is based on a piezoelectric crystal whose resonant frequency is sensitive to tiny changes in its mass—it can sense a change of 10-1° g/cm2. In one use of this device as a detector it was coated with a thin film of zeolite, a silicate mineral. Zeolite has intricate passages of a very uniform size. Thus it can act as a molecular sieve, allowing only molecules of a certain size to pass through onto the detector, where their accumulation changes the mass and therefore alters the detector frequency. This sensor has been used to detect amounts of methyl alcohol (CH3OH) as low as 10 9 g. 

Diamondlike Carbon and Hard Carbon-Based Sensors Sensors that are based upon diamond technology include thermistors, pressure and flow sensors, radiation detectors, and surface acoustic wave devices [103]. The relative ease of depositing prepattemed, dielectrically isolated insulating and. semiconducting (boron-doped p type) diamond films has made polycrystalline diamond-based sensors low-cost alternatives to those based on conventional semiconductors. Diamondlike carbon and diamond films synthesized by chemical... 

S T SAW SCPE SECNAV SORTS SRBSDS SWAT science and technology surface acoustic wave shipboard collective protection equipment Secretary of the Navy Status of Resources and Training System short-range biological detector system special weapons and tactics team... 

An example of one of TSA/TSL s R D funded MEMS based project is the Sandia National Laboratories (SNL) MicroHound project. This is based on the SNL Micro Chem Lab on a Chip , illustrated in Figure 1. The original prototype system from SNL was developed for high vapour pressure, chemical weapons (CW) detection, which utilized a MEMS GC separator, with miniature surface acoustic wave (SAW s) based sensors. The system included an inlet, coated pre-concentrators, detectors, and pumps. To make this useful for trace explosives detection, the addition of an alternate front-end sample collection/macro-preconcentrator and MEMS based coated-preconcentrator is necessary, along with the option to utilize or exclude the MEMS GC separator followed by detection by either, or both, SAW s and miniaturized IMS detectors. 

Hill and Martin (2002) presented a review of conventional analytical methods for CWAs. They discussed various. sensors, such as surface acoustic wave sensors, electrochemical sen.sors, spectrophotometric sensors, immunochemical sen.sors, and IMS detector. For OP nerve agents. FPD and MS are the detectors of choice when coupled with GC or LC. Miniature ion trap ma.ss spectrometer has been described for the detection of nerve agents in the field (Patterson et at., 2002 Riter et al., 2002). A book published by the Institute of Medicine and the National Research Council explains the use of various types of detectors for nerve agents as well as CWAs (lOM, 1999). 

---