Based Sensors

A new chemical sensor based on surface transverse device has been developed (99) (see Sensors). It resembles a surface acoustic wave sensor with the addition of a metal grating between the tranducer and a different crystal orientation. This sensor operates at 250 mH2 and is ideally suited to measurements of surface-attached mass under fluid immersion. By immohi1i2ing atra2ine to the surface of the sensor device, the detection of atra2ine in the range of 0.06 ppb to 10 ppm was demonstrated. 

Thermal Methods Level-measuring systems may be based on the difference in thermal characteristics oetween the fluids, such as temperature or thermal conductivity. A fixed-point level sensor based on the difference in thermal conductivity between two fluids consists of an electrically heated thermistor inserted into the vessel. The temperature of the thermistor and consequently its electrical resistance increase as the thermal conductivity of the fluid in which it is immersed decreases. Since the thermal conductivity of liquids is markedly higher than that of vapors, such a device can be used as a point level detector for liquid-vapor interface. 

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

Novel glycerol and formaldehyde selective sensors based on pEI-Sensitive Field Effect Transistors as transducers and Glycerol Dehydrogenase and Formaldehyde Dehydrogenase as biorecognition elements have been developed. The main analytical parameters of the sensors have been investigated and will be discussed. 

SENSORS BASED ON FREE-STANDING MOLECULARLY IMPRINTED POLYMER MEMBRANES. COMPUTATIONAL MODELLING OF SYNTHETIC MIMICKS OF BIORECEPTORS... 

DEVELOPMENT OF A DNA SENSOR BASED ON ALKANETHIOL SELF-ASSEMBLED MONOLAYER-MODIFIED... 

NOVEL OPTICAL pH SENSORS BASED ON CATECHOL AZO DYE DERIVATIVES... 

FIGURE 13.55 (sensor based on an elecmcalty tunable micromachined Eabry-Perot interferomeced and (b) the siitfcing of the pass band controlled by the tuning voltage. ... 

Figure 13.55 shows the principle of a gas sensor based on an electrically tunable micromachined Fabry-Perot interferometer, and the shifting ol the pass band controlled by rhe tuning voltage. 

For example, Novasina S.A. (www.novasina.com), a Swiss company specializing in the manufacture of devices to measure humidity in air, has developed a new sensor based on the non-synthetic application of an ionic liquid. The new concept makes simple use of the close correlation between the water uptake of an ionic liquid and its conductivity increase. In comparison with existing sensors based on polymer membranes, the new type of ionic liquid sensor shows significantly faster response times (up to a factor of 2.5) and less sensitivity to cross contamination (with alcohols, for example). Each sensor device contains about 50 pi of ionic liquid, and the new sensor system became available as a commercial product in 2002. Figure 9-1 shows a picture of the sensor device containing the ionic liquid, and Figure 9-2 displays the whole humidity analyzer as commercialized by Novasina S.A.. 

Fisk, B., and de Almeida, A. T. (1998). Sensor-Based Demand Controlled Ventilation. Energy and Buildings 29(l) 35-44. 

FIGURE 6-15 Schematic representation of the ion permeability modulation for cation-responsive voltammetric sensors based on negatively charged lipid membranes. Complexation of the guest cation to the phospholipid receptors causes an increase of the permeability for the anionic marker ion. (Reproduced with permission from reference 49.)... 

FIGURE 6-20 Configuration of a penicillin sensor based on an microarray electrode coated with a pH-responsive polypyrrole. Vq = gate voltage VD = drain voltage ID = drain current PS = potentiostat CE and RE = counter and reference electrodes, respectively. (Reproduced with permission from reference 76.)... 

Inertial sensors based on atom interferometer basic principle... 

A very recent example of the first case is presented by Vilaseca et al. [71] where an LTA coating on a micromachined sensor made the sensor much more selective to ethanol than methane. Moos et al. [72, 73] report H-ZSM5 NH3 sensor based on impedance spectroscopy using the zeolite as active sensing material. At elevated temperatures (>673 K) NH3 still adsorbs significantly in contrast to CO2, NO,... 

Sensor-based methods. Whilst many methods use sensors, the simplest being temperature measurement, this terminology is often used to cover viscosity, pH, oxygen and humidity determination, etc. These are true in-line techniques and offer rapid, inexpensive real-time analysis. Humidity determination in drying ovens is a common example. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Bariain, C Matias, I.R., Fdez-Valdivielso, C Elosiia, C Luquin, A., Garrido, J. and Laguna, M. (2005) Optical fiber sensors based on vapochromic gold complexes for environmental applications. Sensors and Actuators B, 108, 535—541. 

Matsubara, K., Kawata, S. and Minami, S. (1988) Optical chemical sensor based on surface plasmon measurement Appl. Opt., 27, 1160-1163. 

The ISFET is an electrochemical sensor based on a modification of the metal oxide semiconductor field effect transistor (MOSFET). The metal gate of the MOSFET is replaced by a reference electrode and the gate insulator is exposed to the analyte solution or is coated with an ion-selective membrane as illustrated in Fig. 

D. Wienke, T. Vijn and L. Buydens, Quality self-monitoring of intelligent analyzers and sensor based on an extended Kalman filter an application to graphite furnace atomic absorption spectroscopy. Anal. Chem., 66 (1994) 841-849. 

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