Receptors, sensor materials

Fluorescent SAMs on glass have been developed by Crego-Calama et al. as new sensor materials. In 1999, the phenomenon of proximal but spatially separable receptor-fluorophore communication was recorded in solution by Tonellato et al.33 and in 2001 Crego et al. demonstrated for the first time that disconnection between fluorophore and receptor can be applied to the preparation of stable sensitive fluorescent materials for metal ion sensing.34 They used SAMs on glass substrates as a 2D scaffold to impart sufficient molecular orientation to separately deposit various binding functionalities (rather than the entire receptor molecule) and the fluorophore on the surface to achieve analyte selectivity. This approach avoids the synthesis and... 

Cinchona-Based Sensors, Receptors, and Materials for Separation and Analytics 4SS... 

The analyte can hardly be identified if the sensor substrate induces only weak and unspecific interactions. A new approach to overcome these problems is the development, using supramolecular chemistry, of sensor materials which allow the production of selective chemosensors. A large number of supramolecular receptors can be prepared by means of combinatorial chemistry [12], but the selective receptors described so far, such as cyclodextrins and calixarenes, offer only a relatively small number of distinct variations. 

The value of dn/dC depends on the properties of the material, e.g., in case of proteins this coefficient is 0.188 ml/g35 and in case of glucose dissolved in water (used for calibration measurements as discussed later in this chapter) this coefficient is 0.069 ml/g36. In the second mode of operation, analytes bind to the sensor surface (e.g., mediated by a receptor layer). In this case a thin layer with thickness w and refractive index nw is formed by the adsorbed analytes. Because the value of nw (e.g., 1.45 for proteins) is usually different than the refractive index of the solution (e.g., 1.33 for water) that contains the analyte molecules, a phase change is induced. The average layer growth (Aw) on the sensor surface can be related to the mass change (Am) per surface area (A) ... 

The dominant attribute that has driven interest in fluorescent conjugated polymers (CPs) sensory materials is their ability to produce signal gain in response to interactions with analytes. The increased sensitivity (amplification) is derived from the ability of a conjugated polymer to serve as a highly efficient transport medium of electronic excitation. Analyte specificity in CP-based sensors results from the covalent or physical integration of receptors, imprinting, and/or the CP s overall electrostatic and chemical characteristics. The observed amplification is a... 

The human body, for instance, has sensors (eyes, ears, touch receptors in the skin, and so forth), a controller (the brain), and actuators (muscles) to react and respond to commands. These are the same basic concepts as the adaptive systems discussed in this chapter. Robots today, such as the welding machines used in industry or the toy dogs sold as pets, are extremely Umited in mobility and adaptability compared to humans. Yet smart materials, along with a design based on the sensory, nervous, and muscular systems of the body, could one day create an agile and adaptable robot. 

While the variety of NPs used in catalytic and sensor applications is extensive, this chapter will primarily focus on metallic and semiconductor NPs. The term functional nanoparticle will refer to a nanoparticle that interacts with a complementary molecule and facilitate an electrochemical process, integrating supramolecular and redox function. The chapter will first concentrate on the role of exo-active surfaces and core-based materials within sensor applications. Exo-active surfaces will be evaluated based upon their types of molecular receptors, ability to incorporate multiple chemical functionalities, selectivity toward distinct analytes, versatility as nanoscale receptors, and ability to modify electrodes via nanocomposite assemblies. Core-based materials will focus on electrochemical labeling and tagging methods for biosensor applications, as well as biological processes that generate an electrochemical response at their core. Finally, this chapter will shift its focus toward the catalytic nature of NPs, discussing electrochemical reactions and enhancement in electron transfer. 

NPs provide highly efficient catalysts and sensors due to their unique chemical and physical properties. NPs can be used as exo-active surfaces where a multitude of molecular receptors can bind analytes and generate a signal. Alternatively, NPs can be used as core-based materials in which biocatalytic processes can activate their core or they provide a biologically inert electrochemical label. As catalysts, NPs utilize their large surface area to volume ratio and enhance either electrochemical reactions or electron transfer at an electrode. The use of NPs in catalysts and sensors will continue as these functional materials serve as active units within these applications. 

One method to realize the taste sensor may be the utilization of similar materials to biological systems as the transducer. The biological membrane is composed of proteins and lipids. Proteins are main receptors of taste substances. Especially for sour, salty, or bitter substances, the lipid-membrane part is also suggested to be the receptor site [6]. In biological taste reception, taste stimulus changes the receptor potentials of taste cells, which have various characteristics in reception [7,8]. Then the pattern constructed of receptor potentials is translated into the excitation pattern in taste neurons (across-fiber-pattem theory). 

Similarly to their natural counterparts (enzymes, antibodies, and hormone receptors), MIPs have found numerous applications in various areas. They have been used as antibody mimics in immunoassays and sensors and biochips as affinity separation materials and for chemical and bioanalysis, for directed synthesis and enzyme-like catalysis, and for biomedical applications. Concerning their commercialization, there has been great progress during the past decade, in particular in the... 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

In aspect of chip-based technology, electrochemical genosensors based on different materials and transducers have been recently developed in response to clinical demand of giving promising results [18-25]. Different sensor technologies provide a unique platform in order to immobilize molecular receptors by adsorption, crosslinking or entrapment, complexation, covalent attachment, and other related methods on nanomaterials [5,7,26]. 

For the application of label-free optical transduction principles like SPR or RIfS, a chiral receptor bound to a transparent polymer layer is required. As various types of these polymers have already been applied to chromatographic separation processes, a substantial wealth of knowledge was achieved during the last few decades. Stationary materials like bonded amide selectors or cyclodextrins were adopted as sensor coatings. Several different applications of these materials in various fields of interest have been reported in the literature [17]. 

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