Properties sensing

TDAG8 appears restricted to the immune system. As tissue inflammation is usually followed by local hypoxia and acidosis, the pH-sensing property of TDAG8 appeared of particular interest in this context. Unexpectedly, however, the phenotype of mice... 

Brown P.H., Bruckenstein D.A., Han-VEY J.C., et al.An assessment of the anti-sense properties of RNase FI-competent and steric-blocking oligomers. Nucleic Acids Res. 1995 23 1197-1203. 

Li, Y Su, X., Jian, J. and Wang, J. (2010) Ethanol sensing properties of tungsten oxide nanorods prepared by microwave hydrothermal method. Ceramics International, 36, 1917-1920. 

Fig. 5 Two-stage sensing property via a conjugated donor-acceptor-donor constitution of BHPN (reprint from ref. [58], Copyright 2005 American Chemical Society)...

A major advantage of fluorescence as a sensing property stems from the sensitivity to the precise local environment of the intensity, i.e., quantum yield (excited state lifetime (xf), and peak wavelength (Xmax). In particular, it is the local electric field strength and direction that determine whether the fluorescence will be red or blue shifted and whether an electron acceptor will or will not quench the fluorescence. An equivalent statement, but more practical, is that these quantities depend primarily on the change in average electrostatic potential (volts) experienced by the electrons during an electronic transition (See Appendix for a brief tutorial on electric fields and potentials as pertains to electrochromism). The reason this is more practical is that even at the molecular scale, the instantaneous electric... 

From Figure 13 it can be seen a typical example demonstrating the influence of the properties of the fibre coating on fibre sensing properties. 

Porous ultrafine tin oxide ethanol gas sensors92 in the form of a thin film have been prepared from tin alkoxide by the sol-gel process. The microstructural evolution of the tin oxide films, which affected the ethanol gas-sensing properties of the films, was investigated as a function of firing temperature and solution concentration. Theoretically, it was expected that ethanol gas sensitivity would increase monotonically with decreasing film thickness, but experimental results showed a maximum sensitivity at about 70 nm. The sudden decrease of the sensitivity below the thickness of 70 nm seemed to be due to the sudden decrease of film porosity, i.e., the sudden decrease of the number of the available sites for the oxidation reaction of ethanol molecules. Thus, it seemed that below the thickness of 70 nm, the sensitivity was governed by microstructure rather than by film thickness. 

SILAR-grown ZnO films have been tested for gas sensor applications.29 The ZnO films, doped with tin for this purpose, were grown from a mixture of dilute zinc sulfate, sodium hydroxide, and sodium tin(IV)oxide solutions. The final step, resulting in the oxide film, was treatment of the substrate and film in a nearly boiling water bath. The N02 gas sensing properties were tested for films doped with Al, Cu, Pd, and Sn, but only the film doped with tin exhibited sensitivity toward N02. The sensitivity of the ZnO Sn film was 5% /ppm after rapid photothermal processing (RPP). The best sensitivity was obtained when the tin concentration was 5-10%.29... 

Figure 1.12 Photochemical titration curves of crystal violet co-entrapped in silica sol-gel matrices with different surfactants, no surfactant ( ) and in solution (x) show the impressive variations in the sensing properties for the same entrapped dye. (Reproduced from ref. 26, with permission.)... 

As an example of the use of array methodology to study chemical sensor properties let us consider the thirteen molecular structures reported in Figure 5. To investigate the sensing properties of these molecules we studied the behaviour of the response of thickness shear mode resonators (TSMR) sensors, each coated with a molecular film, to different concentration of various volatile compounds (VOC). Analyte compounds were chosen in order to have different expected interaction mechanisms. 

Dye-doped polymeric beads are commonly employed in different formats (Fig. 5), namely as water-dispersible nanosensors, labels and in composite materials (DLR-referenced and multianalyte sensors, sensor arrays, magnetic materials, etc.). The sensing properties of the dye-doped beads are of little or no relevance in some more specific materials, e.g., the beads intended for photodynamic therapy (PDT). The different formats and applications of the beads will be discussed in more detail in the following section, and the relative examples of sensing materials will be given. 

M. Stankova, X. Vilanova, E. Llobet, J. Calderer, C. Bittencourt, J. J. Pireaux, and X. Correig, Influence of the annealing and operating temperatures on the gas-sensing properties of rf sputtered WO3 thin-film sensors. Sensors Actuators 105(2), 271—277 (2005). 

We recently published a chapter in the book Silicon Carbide Recent Major Advances by Choyke et al. [19] that describes SiC gas sensor applications in detail. In this book, we emphasize device properties applications are only briefly reviewed at the end. The device and gas sensing properties of various field-effect chemical gas sensing devices based on SiC are described, and other wide bandgap material devices are reviewed. The detection principle and gas response is explained, and the buried channel SiC-FET device is described in detail. Some special phenomena related to the high-temperature influence of hydrogen at high temperature are also reported. 

It is important to have a clear picture of the detection mechanism before we introduce the different types of field-effect transistor (FET) devices and their gas sensing properties. The sensing mechanism is largely independent of the device type, since the chemical reactions responsible for the gas response are defined by the type of catalytic material processed onto the device and the operation temperature [1,2, 20, 21]. Even at a temperature of 600°C, chemical reactions occur on the catalytic metal surface at a rate of a few milliseconds, which is slower than the response time of the devices. 

The p-n junction diodes employing catalytic metal contacts have recently been tested for their gas-sensing properties [66, 67]. The catalytic metal contact was placed directly on the semiconductor in this device, as shown in Figure 2.6. In general the response appears to be lower than for the traditionally used devices described earlier in this section. However, this means that for any catalytic metal used as an ohmic contact to a p-n junction, it can be expected that the /-Vcharacteristics will be influenced, for example, in a hydrogen-containing atmosphere. 

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