Receptors chemical sensors

There are three advantages to study molecular recognition on surfaces and interfaces (monolayers, films, membranes or soHds) (175) (/) rigid receptor sites can be designed (2) the synthetic chemistry may be simplified (J) the surface can be attached to transducers which makes analysis easier and may transform the molecular recognition interface to a chemical sensor. And, which is also a typical fact, this kind of molecular recognition involves outside directed interaction sites, ie, exo-receptor function (9) (see Fig. 5b). 

Figure 2. Classification of chemical sensors according to the operating principle of the receptor and transducer.

Figure 3. Components of an ion-selective electrode chemical sensor (left) and photographs of electrode body (right) showing electrode barrel with silver-silver chloride electrode, and screw-on electrode tip with end-clip for attaching the PVC membrane containing immobilised molecular receptors that will selectively bind specific target species.

Panasyuk TL, Mirsky VM, Piletsky SA, Wolfheis OS. Electropolymerized molecularly imprinted polymers as receptor layers in a capacitive chemical sensor. Anal Chem... 

In spite of all their advantages, sensitivity and selectivity, bio-sensors, however, do possess disadvantages connected with thermal and timely instability, high cost of bio-receptors and the need to add substrates in the solution under analysis as signal-generating substances. Some attempts to synthesize and use as receptors chemical organic catalytic systems, which will ensure the required selectivity and response rate, have become the basis for developing enzyme-free sensors [11], or biomimetic sensors. 

As with the majority of ISEs, all of the aforementioned receptors are immobilised within close proximity to the transducer element. However, conducting polymers (electroactive conjugated polymers) are now emerging rapidly as one of the most promising classes of transducer for use within chemical sensors. Here, the receptor can be doped within the polymer matrix, i.e. within the transducer element itself. This will facilitate the production of reliable, cost-effective, miniaturised anion-selective sensors, as it will be possible to move away from plasticiser-based membranes, but allow for ion recognition sites in conjunction with all-solid-state ion-to-electron transducers. 

Interest in the development of synthetic schemes and approaches to create molecular recognition elements has blossomed during the past half century for a number of reasons. In contrast to biologically based receptors, artificial mimics have the potential advantages of being less costly, more stable, and better able to withstand harsher conditions.7-12 Furthermore, synthetic methodologies can be used to create receptors for molecules for which an artificial receptor does not exist. These designer materials have enormous potential in catalysis, clinical and pharmaceutical applications, chemical sensors, separation science, and electronics.7-12... 

Although, the main emphasis of this chapter lies on the fundamental aspects of calixpyrrole-fluoride complexation reactions, with the major part being devoted to the thermodynamic properties of these systems, calixpyrrole receptors seem to be promising for the development of chemical sensors and for the removal of fluorides from water. They also show promise for the separation of anion substrates. 

As far as chemical sensors are concerned, colorimetric chemosensors for anions based on calix[4]pyrrole (16-18, 22-31) showed strong binding to the fluoride anion. Receptors (29-31) are the first naked-eye detectable chemosensors that are able to discriminate between different anionic substrates as a result of detectable colour changes. On the other hand, the fluorescence of the receptors (16-18, 22-28) is quenched significantly in the presence of anionic guests. 

A chemical sensor is a device that transforms chemical information into an analytically useful signal. Chemical sensors contain two basic functional units a receptor part and a transducer part. The receptor part is usually a sensitive layer, therefore a well founded knowledge about the mechanism of interaction of the analytes of interest and the selected sensitive layer has to be achieved. Various optical methods have been exploited in chemical sensors to transform the spectral information into useful signals which can be interpreted as chemical information about the analytes [1]. These are either reflectometric or refractometric methods. Optical sensors based on reflectometry are reflectometric interference spectroscopy (RIfS) [2] and ellipsometry [3,4], Evanescent field techniques, which are sensitive to changes in the refractive index, open a wide variety of optical detection principles [5] such as surface plasmon resonance spectroscopy (SPR) [6—8], Mach-Zehnder interferometer [9], Young interferometer [10], grating coupler [11] or resonant mirror [12] devices. All these optical... 

Electrochemical sensors — Electrochemical sensors belong to the family of chemical sensors. Chemical sensors are devices that convert chemical information (concentration, - activity or partial pressure of the analyte) into a measurable signal. Chemical sensors contain two basic functional units a receptor and a transducer. The receptor interacts with the analyte and transforms chemical information into a form of energy that is converted further by the transducer into a useful analytical signal. 

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