Sensing schemes

The ion sensing scheme based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) was extended to other anions. Both the clinically significant chloride ion124 and the environmentally important nitrate anion125 can be sensed in the desired concentration ranges. Such sensors have the unique advantage of having a virtually pH-insensitive response. 

Sensing schemes have become reliable enough to be of practical utility, instrumentation has become available at costs that make this sensor technology competitive to established sensors, and numerous other sensors schemes have been presented that are of interest, at least from an academic point of view. 

Many compounds exhibit near-IR and mid-IR absorption. By using IR transparent optical fibers, detection of an absorption band in the IR region is possible for optical sensing. Both direct sensing using the absorption property of the analyte or indicator sensing are widely exploited. Most mid-IR sensing schemes are based on the principles of internal reflection spectroscopy, or the attenuated total reflection (ATR) [3,14-21],... 

ICT probes thus do not play a role as pH-indicators. However, this fact can be utilized for powerful sensing schemes in a different context, see Sect. 4.1.1. 

As can be summarized from this survey dye-doped beads represent very versatile analytical tools which are applied in various fields of science and technology. The size of the particles is of the utmost importance here. The smallest beads are mostly designed for intracellular monitoring of analytes and much larger beads are often used in composite materials and sensor arrays. Sensing schemes for optical che-mosensors are established and are similarly realized on nano- and microscale. 

The intermolecular cycloaddition route to spirocyclopropyl isoxazolidines and their subsequent rearrangement, used so widely by Brandi and co-workers (372-375) (Schemes 1.16 and 1.17, Section 1.5), has also been achieved in an intramolecular sense (Scheme 1.72). Cycloaddition of the alkenyl nitrone reagents (333a-c) afforded bicyclic isoxazolidinyl adducts 334, which rearranged under thermolysis in analogous fashion to the earlier work to give piperidinones (335) via... 

Many chromophore reagents are available for that purpose. Therefore, selectivity to a very large extent depends on the materials and optical components that allow us to deliver the light and manipulate it as needed in one or another optical sensing scheme. 

Optochemical sensors have had a huge expansion during the last few years, and surely the main reason is the wide range of optical phenomena that one can take advantage of for the design of different sensing schemes. 

Simple IWAO sensing schemes have been designed following the optical response towards different analyte activities depending on the ionophore employed and keeping constant the solution pH. 

The majority of Os(II) complexes exhibit weak luminescence and might not appear to be attractive candidates for use in various sensing schemes based on luminescence. Systems serving as oxygen sensors, including Os(II) complexes, have recently been reviewed [105]. Nonetheless, there are a few recent examples of applications of this sort and one recent application of a Ru(II)/Os(II) energy transfer based sensing system. 

One of the most widely researched enzymatic sensing schemes relies on GOx-catalyzed oxidation of glucose in the following reaction 14... 

Further progress in the development of sensing systems based on silica nanoparticles was achieved by doping with fluorescent probes. In these systems, the nanoparticles act as transporters delivering the probe across membranes into the cell, thus improving both performance and protection from matrix interferences.19-22 As we will see later, the possibility to confine several probes and dye molecules within the same particle also allows the design of more complex sensing schemes. 

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