Sensing matrix

Kwast, K.E., and S.C. Hand (1996). Acute depression of mitochondrial protein synthesis during anoxia Contributions of oxygen sensing, matrix... 

Generally, having a repetitively renewable sensing matrix is of great importance to a successful biosensor. In fact, most of the matrices presented in this contribution can be easily regenerated by harsh or mild regeneration conditions [11,16,18,25,26],... 

To provide a sensing matrix that can use the least acidic proton on citric acid, polyethyleneimine, with p/sTa =11, serves as the matrix onto which citric acid wiU be ionically tethered to the polymer s backbone. Titration of a solution of polyethyleneimine with a solution of citric acid to a pH of 6.0 produces a polymer solution of polyetheneimine-citric acid, where the lone least-acidic proton is on the citric acid available for reaction with the ammonia, while the other two are bound to the amines of the backbone of the polyethyleneimine. For a reference arm, another solution of polyethyleneimine is titrated with a solution of citric acid to a pH of 8, thereby yielding a solution in which all the protons of the citric acid are on the polyethyleneimine backbone. The first solution, pH 6.0, is deposited on the sensing arm of a silicon nitride waveguide. The second solution, pH 8.0, is deposited on the reference... 

As it is known, Sn02 gas response has the chemisorption nature independently from the type of detected gas. However, we have found out that film thickness had different influence on gas response to ozone and H2 (Fig. 2b). It testifies that different elements of gas sensing matrix control the gas response during O3 and H2 detection. 

Temperature compensation is obviously an issue for a technology where the conductivity of the material can affect the results. After 10 years of use, this problem has been extensively explored. The sensing matrix includes temperature sensors, and the software has a sophisticated temperature compensation algorithm. The area is typically insulated to avoid effects from changes in external temperature. The results are not affected by the hot environment itself or even temperature differentials in the monitored piece, as long as temperature conditions are relatively comparable between measurements. It is therefore standard operating procedure to take all measurements after the actual location has reached its operating temperature. 

A European chemical factory had corrosion/erosion problems in an inlet pipe, particularly weld corrosion. Traditional UT was seen to be unreliable because the uneven surfaces and varying wall thickness (not to mention the cramped space) made it a very challenging task for even the most experienced UT operator. Equipping the inlet with a sensing matrix allows the factory to regularly inspect for the onset of corrosion, with more intensive inspection if corrosion occurs. UT is also difficult to apply in high temperature. 

Nanocomposites also provide more possibilities for control of the catalytic activity of the sensing matrix. For example, it has been shown that the introduction of TiO nanoparticles into the polymer matrix of poly(/t-phenylenevinylene) (PPV) changes the adsorption properties of the matrix. Adsorption of oxygen was found to be stronger on the PPY-TiO nanocomposite than on pure PPV (Baraton et al. 1997). In some cases, a catalyst incorporated in the conducting polymer film can help in detecting some inert analytes. Conducting polymers have difficulties with detection inert analytes. 

Insulating polymer—black carbon Chemiresistors Polymer—gas-sensing matrix, sweUing effect... 

Insulating polymer-CNTs Chemiresistors (sensing Polymer—gas-sensing matrix,... 

Polymer-black carbon (PMMA, Chemiresistors (sensing Poiymer—gas-sensing matrix, swelling effect... 

Metal oxide-noble metals Chemiresistors (sensing Metal oxide—gas-sensing matrix... 

Fig. 20.1 Schematic diagram iUustrating the change of the geometry of intergrain contacts in gas-sensing matrix during annealing (a) the structure of as-deposited films, (b) after sintering...

Size and Shape of the Grains That Formed a Gas-Sensing Matrix Should Be Controlled... 

For many years, almost all the work on NH4+ ISEs focused on the macrocyclic antibiotics nonactin (NH4+-I) and monactin (NH4+-II), see Figure While the type of sensing matrix has some effect on the selectivities of ISEs based on these ionophores, an approximately 10-fold selectivity over K+ and an approximately 100-fold selectivity over Na+ is characteristic for these sensors. Only in recent years several interesting alternatives have been proposed. Significant improvements of the selectivity of either Na+ or K+ have been obtained by use of rigid crown ethers with bulky substituents that block complexation with larger ions (e.g.,NH4+-III), a... 

Fig. 2.26 Influence In203-Sn02 mixed metal oxide composition on (1, 2) sensor response and (3) specific surface area of gas-sensing matrix calcined at 600 °C (1) response to 1,000 ppm of CO at Tpg =250 °C and (2) response to 450 ppm of NO2 at Tp =150 °C (Adapted with permission from Aifan et al. (2006). Copyright 2006 Elsevier)...

It is mentioned above that, in gas sensors, polymers can be used as the sensing layer or as the transducer itself. Polymers can form selective layers in which the interaction between the analyte and the sensing matrix generates a primary change in a physical parameter in the transduction mechanism. Polymers can also form different membranes, providing selectivity of chemical reactions in electrochemical gas sensors. 

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