Sensing principles

Many classical optical sensing principles, which are well known from free space optics can be implemented in integrated optical structures, while integrated optics at its turn can act as source of new principles. Many types of integrated optical sensors have been investigated and demonstrators have been realized, mostly at universities and other research institutes. And also at... 

Ion-selective electrodes are now well understood in terms of the underlying theory, and this has made it possible for new sensing principles to emerge that make use of the thousands of chemical receptors originally developed for ion-selective electrodes. One is the field of optical sensors, which has not been discussed here because it is outside the focus of this chapter. Such so-called bulk optodes do not require electrical connectivity between the sensing and detection unit and are therefore more easily brought into various shapes and sizes, including particle formats, which suit the need of modem chemical analysis. 

Biosensors normally offer highly specific molecular recognition reactions like enzyme/substrate-, antigen/antibody-, DNA/DNA-, or protein-interactions [67]. Due to their specific sensing principles and set-up they are limited to special applications and boundary conditions. The limited stability and reproducibility of these devices requires higher standards of maintenance and recalibration. 

It is worth to stress that in contrast to bare LPGs, where the basic sensing principle is the evanescent interaction with the surrounding environment, here the sensing mechanism relies on a guided wave interaction with the overlay. 

Horvath, R. Skivesen, N. Pedersen, H. C., Measurement of guided lightmode intensity An alternative waveguide sensing principle, Appl. Phys. Lett. 2004, 84,4044 4046... 

Fig. 20a. 10. Schematic of the sensing principle of a urea optical sensor based on an ammonium-sensitive membrane employing anionic dye and neutral carrier.

Another principle, which we might call the "common sense principle" for immersed objects, is one we ve used in the last two problems ... 

The Seebeck coefficients Qa and <2b are material constants of conductors A and B, respectively. They depend primarily on two parameters their work function (see Appendix C) and their thermal conductivity. There are many combinations of electronic conductors producing V of few mV °C 1. It is interesting to note that direct modulation of one or both Seebeck coefficients by chemical interaction with an electron acceptor or electron donor gas is possible. It has been demonstrated as a sensing principle for detection of gaseous NO2 with an ti Oj/Au thermocouple junction (Liess and Steffes, 2000). 

This sensing principle does not truly belong to the reflectance category. It is included here only because it does not fit better in any other place. Yet, its operation is interesting and important. It is a cross between the optical and electrochemical... 

Explain the connection between the attenuation loss of the optical fiber used for transmission of information and the sensing principles utilizing an evanescent field. 

Due to the proposed elementary steps of this sensing principle and the signal transduction from the surface reaction to a change of band structure and consequentially, to a change of resistance, as described in detail in (Weimar, 2002), the dependency of the sensor resistance from the concentration of analyte is logarithmic and the resistance change is dependent on the baseline value. In order to have a more transferable parameter for the characterization of sensor performance, the sensor signal S is defined as ... 

When working with sensors, one of the most important issues is cross-sensitivity. Due to the sensing principle, this notably affects metal oxide gas sensors, especially in the case of measurements performed in real life conditions. To prove real life feasibility, it is necessary to keep as close as possible to the real life conditions of the application. In the present case, the real life conditions are mainly represented by the use of ambient air as a carrier gas, but also by the chosen experimental set up. 

The polymer materials not only act as supports for the dye and other necessary additives in the sensing phase, providing protective covering for the transduction element polymers also play various roles in chemical sensors. They provide a compatible environment for the indicator molecules, maintaining or improving the appropriate photophysical features (compared to those observed in homogeneous solution) on which the sensing principle is based. In many cases they collect and concentrate the analyte molecules on sensor surfaces. In addition, the polymer can play an important role in the sensitivity and selectivity of an optical sensor, and its interactions with indicator and analyte molecules influence the analytical performance of the device. 

The principle of calorimetry is very interesting for biological applications. Calorimetric biosensors are based on the detection of the heat production of biological reactions which is caused by enthalpy changes. The micro calorimetric sensing principle is very versatile because of the exothermic nature of nearly all enzymatic reactions [8] and was introduced as a conventionally constructed device very early [9] ... 

Potentialities of the Fluorescent PET Sensing Principle for Molecular Association Research... 

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