Sensors potentiometric recognition

An ideal sensor recognizes analytes in a sensitive, selective, and reversible manner. This recognition is in turn reported as a clear response. In recent years, conducting polymers have emerged as practical and viable transducers for translating analyte-receptor and nonspecific interactions into observable signals. Transduction schemes include electronic sensors using conductometric and potentiometric methods and optical sensors based on colorimetric and fluorescence methods [1]. 

Ciosek et al. (2005) used potentiometric ion-selective sensors for discriminating different brands of mineral waters and apple juices. PC A and ANN classification were used as pattern recognition tools, with a test set validation (Ciosek et al., 2004b). In a subsequent study, the same research group performed the discrimination of five orange juice brands, with the same instrumental device. A variable selection was performed, by means of strategies based on PCA and PLS-DA scores. The validation was correctly performed with an external test set. 

Dias and coworkers utilized an array of potentiometric sensors for the classification of honey samples from different Portuguese regions with respect to the predominant pollen type Erica, Echium, Lavandula. PCA and LDA were employed for the pattern recognition (see Fig. 2.25), after having verified that the variables followed a normal distribution. Cross-validation was applied for evaluating the classification rules, obtaining satisfactory prediction abilities for two classes (about 80%) and poor results for the third one (about 50%) (Dias et al., 2008). 

In a further study, Dias et al. (2009) studied the deployment of a potentiometric electronic tongue based on an array of 36 sensors, for the recognition of the basic taste sensations and for the detection of fraudulent additions of bovine milk to ovine milk. The signals were processed by means of PCA and LDA (see Fig. 2.26), and the classification rules were evaluated by means of cross-validation. The results presented are excellent for fitting but not very satisfactory for prediction. 

Materials with selective binding or transport properties will have a major impact on sensor design and fabrication. Selectivity in either binding or transport can be exploited for a variety of measurement needs. This selectivity can be either intrinsic, that is, built into the chemical properties of the material, or coupled with selective carriers that allow a non-selective material to be converted into a selective one (see the section on recognition chemistry). An example of the latter is the use of valinomycin as a selective carrier in a polyvinyl chloride membrane to form a potentiometric potassium ion sensor. Advances in the fields of gas separation materials for air purification and membrane development for desalinization are contemporary examples illustrating the importance of selective materials. As these materials are identified, they can be exploited for the design of selective measurement schemes. 

It is the aim of this chapter is to present the efforts made worldwide for the development of chemical sensors based on the unique chemical recognition capabilities of organotin structures. In particular, we will examine in a time-based flowchart the progress of the design and application of Sn(IV)-based ionophores and their application in the development of anion selective chemical potentiometric sensors. 

On the other hand, the molecular recognition by enzymes, which are also applied in the form of organelles, microorganisms and tissue slices, is accompanied by chemical conversion of the analyte to the respective products. Therefore this type of sensor is termed a metabolism sensor2. The initial state is usually reached when the analyte conversion is complete. With metabolism sensors, under certain conditions cosubstrates, effectors, and enzyme activities can be measured via substrate determination. Amperometric and potentiometric electrodes and thermistors are the preferred transducers, but in some cases optoelectronic sensors have also been used. With biomimetic sensors physical signals such as sound, stress, or light are measured through their ability to... 

The type of molecular recognition reaction determines the form of the transducer used (Table 5.3). Enzymatic reactions often involve an electron transfer. This electrical activity can be measured with amperometric, potentiometric or conductometric sensors. If the bioreaction includes the generation of H+ or OH ions, then a pH sensitive dye in combination with an optical device can be used. For antibody-antigen binding, the mass change on the surface of the transducer can be detected with a piezoelectric device. Exothermic or endothermic reactions can be followed with a temperature sensor. 

Hassan SSM, Kamel AH, Abd El-Naby H. New potentiometric sensors based on selective recognition sites for determination of ephedrine in some pharmaceuticals and biological fluids. Talanta 2013 103 330-6. 

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