Chemical sensors ideal

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. 

Figure 1.4 shows a schematic diagram for the ideal (bio)chemical sensor (one meeting the above requisites as regards the device itself and the analytical information it produces, both of which are obviously mutually related). 

The ideal (bio)chemical sensor should operate reversibly and respond like a physical sensor (e.g. a thermometer), i.e. it should be responsive to both high and low analyte concentrations and provide a nil response in its absence. One typical example is the pH electrode. In short, a reversible (bio)chemical sensor provides a response consistent with the actual variation in the analyte concentration in the sample and is not limited by any change or disruption in practical terms, responsiveness is inherent in reversibility. An irreversible-non-regenerable (bio)chemical sensor only responds to increases in the analyte concentration and can readily become saturated only those (bio)chemical sensors of this type intended for a single service (disposable or single-use sensors) are of practical interest. On the other hand, an irreversible-reusable sensor produces a response similar to that from an irreversible sensor but does not work in a continuous fashion as it requires two steps (measurement and renewal) to be rendered reusable. Figures 1.12 and 1.13 show the typical responses provided by this type of sensor. Note... 

The first group of sensor properties in Fig. 1.15 is concerned with the quality of results obtained in analytical processes involving a (bio)chemical sensor. All of them are obvious targets of analytical tasks [3]. As shown in the following section, the accuracy of the analytical results relies on a high reproducibility or repeatability, a steep slope of the calibration curve (or a low detection or quantification limit) and the absence of physical, chemical and physico-chemical interferences from the sample matrix. Sensors should ideally meet these essential requisites. Otherwise, they should be discarded for routine analytical use however great their academic interest may be. 

In appraising trends in some scientific or technical area, one usually tends to confuse the real and the ideal, i.e. what is being or will foreseeably be achieved and what is actually needed. This conflict also reaches what is discussed in this section, where the two sides are frequently mixed. There follows a description of major general trends in (bio)chemical sensors with explicit exclusion of those involving a specific group of sensor. 

A notable difference between these two relationships is that the Gibbs-Lippmann equation contains one more independent variable parameter, the interfacial charge. It cannot be determined directly. Several unsuccessful attempts to design chemical sensors (e.g., the immunosensor) based on the measurement of adsorbed surface charge have been made. There are no ideally polarized interfaces that are sufficiently ideal to allow such direct measurement of interfacial charge. 

Potentiometric measurements are done under the condition of zero current. Therefore, the domain of this group of sensors lies at the zero-current axis (see Fig. 5.1). From the viewpoint of charge transfer, there are two types of electrochemical interfaces ideally polarized (purely capacitive) and nonpolarized. As the name implies, the ideally polarized interface is only hypothetical. Although possible in principle, there are no chemical sensors based on a polarized interface at present and we consider only the nonpolarized interface at which at least one charged species partitions between the two phases. The Thought Experiments constructed in Chapter 5, around Fig. 5.1, involved a redox couple, for the sake of simplicity. Thus, an electron was the charged species that communicated between the two phases. In this section and in the area of potentiometric sensors, we consider any charged species electrons, ions, or both. 

In the last years increasing research activities in the fields of membrane science [1, 2], chemical sensors [3], confined matter [4] and micro-reaction engineering [5] have evoked a new interest on porous glass membranes. Furthermore, such membranes are ideal model systems for the investigation of transport processes in porous structures. This broad spectrum of applications demands variable texture properties. 

The ability to synthesize carbon nanostmctures, such as fullerenes, carbon nanotubes, nanodiamond, and mesoporous carbon functionalize their surface or assemble them into three-dimensional networks has opened new avenues for material design. Carbon nanostructures possess tunable optical, electrical, or mechanical properties, making them ideal candidates for numerous applications ranging from composite structures and chemical sensors to electronic devices and medical implants. 

The creation of open porous structures with an extremely high surface area is of great technological significance because such structures are ideally suited for electrodes in many electrochemical devices, such as fuel cells, batteries, and chemical sensors.1 The open porous structure enables the fast transport of gases and liquids, while the extremely high surface area is desirable for the evaluation of electrochemical reactions. The electrodeposition technique is very suitable for the preparation of such structures because it is possible to control the number, distribution, and pore size in these structures by the choice of appropriate electrolysis parameters. 

Ideally the sensor should warm up rapidly after power-on, achieving its baseline condition fairly quickly. However, a number of current commercial chemical sensors can take up to 24 h to achieve a stable baseline after long periods of inactivity. Although handheld sensors are often used for short durations, it is preferable to have a sensor that is capable of continuous operation. 

Figure 1 is a schematic representation of the main components of an idealized chemical sensor. The most important part of any chemical sensor is the selective membrane/layer, usually positioned on the sensor tip, which interacts with the sample in such a way as to provide analytically useful information about a particular component, the analyte, in the sample. In order to do this, the interaction of this... 

Like any other type of sensor, the ideal photometric chemical sensor should not perturb the sample. In practice, this requires that the amount of analyte present to react with the indicator reagent should be small compared to the total amount of analyte in the sample. If this requirement is not met, then the contact of analyte with the reagent in the chemical transducer will result in a change in the analyte concentration in the sample. This, in turn, will result in a... 

The ideal chemical sensor would respond instantaneously to the relevant analyte, with high specificity and sensitivity, be usable over a wide range of analyte concentrations and be repeatable. In addition, the ideal sensor device would be inexpensive to produce, simple to use, rugged, and both reusable and recyclable. 

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