Planar sensors, layers

Deposition of sensor layers is possible on fibre Flow-through cell allowing the optics, planar waveguides, and test strips simultaneous exposure of the membrane to... 

We have shown that antiresonant dielectric layers can be used to design low-loss liquid-core waveguides that are suitable for implementing planar sensor device geometries. The following sections will describe in more detail how the design principles laid out here were implemented in silicon-based LC-ARROW chips and used for optical sensing and detection of a wide variety of substances. 

Figure 5 shows the response of a type-A sensor to propane. Several features strike the eye. First, the sensor is quite sensitive propane concentrations as low as 1 ppm are clearly detectable. Flowever, the steady-state response saturates at the same level of R 400 k 2, irrespective of the propane concentration. This is believed to be due to the glass substrate. Such substrate influences have been identified and discussed previously for other planar sensors [6,7]. Glass is an ionic conductor at elevated temperatures, and the equivalent resistance of the current paths through the glass substrate acts in parallel to the resistance R(f) of the IDE sensor proper. The total resistance R, R f ) can never exceed R, . This explanation was corroborated by measurements on a type-A sensor without sensitive layer. 

Fig. 7.1 Commercially available configurations of planar sensors (a, c) double-sided platforms fabricated using thick-film technology (Siemens AG) (b) multisensor platform with customer-specific sensor layers, heater layers, tmd measurement electrodes in mono- and multilayer versions [Reprinted from Heraeus Sensor Technology (http //www. dwmai.com)]...

Square-planar ds platinum complexes could perhaps be used as the chemically sensitive layer for a chemical sensor system. These complexes are robust and form colored solid-state materials that respond spectroscopically to a wide range of volatile organic compounds (VOCs) this process has been named vapochromism. The vapochromic shifts occur in the solid-state UV-vis,... 

In addition, the integration of modem optical technology and electrochemical techniques for sensing applications appears to be a powerful new approach. A new type of optoelectrochemical sensor for chlorine, based on an electrochromic thin-film sensing layer placed on top of a planar waveguide, has demonstrated the applicability of this combined approach. 

The absorption-based platforms described previously employed evanescent wave interrogation of a thin sensing layer coated onto a planar waveguide. A sensitivity enhancement strategy for optical absorption-based sensors based on planar, multimode waveguides was developed recently by us18. The objective was to apply this theory to the development of low-cost, robust and potentially mass-producible sensor platforms and the following section outlines the assumptions and predictions of this theoretical model. 

Simultaneous and continuous measurements of extracellular pH, potassium K+, and lactate in an ischemic heart were carried out to study lactic acid production, intracellular acidification, and cellular K+ loss and their quantitative relationships [6, 7], The pH sensor was fabricated on a flexible kapton substrate and the pH sensitive iridium oxide layer was electrodeposited on a planar platinum electrode. Antimony-based pH electrodes have also been used for the measurement of myocardial pH in addition to their application in esophageal acid reflux detection. 

The geometry shown here corresponds to a semi-infinite planar diffusion. Other geometries (e.g., radial geometries) typical for microsensors can be used. The enzyme-containing layer is usually a hydrogel, whose optimum thickness depends on the enzymatic reaction, on the operating pH, and on the activity of the enzyme (i.e., on the Km). Enzymes can be used with nearly any transduction principle, that is, thermal, electrochemical, or optical sensors. They are not, however, generally suitable for mass sensors, for several reasons. The most fundamental one is the fact... 

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