Lifetime, chemical sensors

A major focus of researchers creating planar CE devices is speed of analysis, in part so that the devices can be used as chemical sensors and circumvent the severe selectivity and lifetime requirements of conventional chemical sensors. To increase the speed of analysis, shorter capillaries should be used, in combination with higher electric field strengths. Optimum efficiency depends on minimization of all unavoidable sources of band broadening, in addition to the elimination of nonideal effects such as Joule heating and adsorption on capillary walls. Therefore, work to understand the contributions which limit the efficiency of the separation is continuing. 

Major Applications pH Sensors, optical chemical sensors, biochemical sensors, biosensors," fluorescent pH detector system, measuring fluorescence lifetime in cells, determining concentration of a laminar sample stream, fluorescent reporter beads for fluid analysis, measuring ch ical analytes, intracellular pH in human sperms, " multidrug resistance," recording intramitochon-drial pH, fluorescent probes ... 

Work on chemical sensors made with planar microfabrication techniques has been ongoing for almost 25 years [1,2]. In that period of time many sensor concepts have been proposed and developed, and some of them have reached the level of commercially available products [3-5]. Yet many difficulties have been encountered in the process of turning microfabricated chemical sensors into useful products such as unreliable packaging low lifetimes lack of wafer-level definition of ion-selective membranes, etc... Due to the efforts of many groups of researchers, solutions to many of these problems are now available to a large extent [6-9]. 

Optical fibers are commonly used for remote monitoring of fluorescent analytes. Fiber-optic chemical sensors can provide both qualitative and quantitative information about the analyte under consideration. Since each analyte has different fluorescent properties, selective measurements can be performed by choosing the correct excitation and emission wavelengths. The fluorescence bands are usually quite broad and the bands for a class of compounds overlap, so it may be difficult to distinguish among them. Fluorescence lifetime measurements are sometimes... 

The use of fiber-optics in the preparation of the optical sensors allows performing spectroscopy measurements at sites that are inaccessible to conventional spectroscopy and also over large distances. Moreover, the possibility of using evanescent wave spectroscopy and spatially resolved lifetime spectroscopy makes FOCS (fiber optics chemical sensors) a very interesting option for building the sensors. Comprehensive reviews [183,184] on fiber-optic chemical sensors are available, where the most interesting applications of sol-gel coatings for optical sensors are described. 

With further understanding how molecular rotors interact with their environment and with application-specific chemical modifications, a more widespread use of molecular rotors in biological and chemical studies can be expected. Ratiometric dyes and lifetime imaging will enable accurate viscosity measurements in cells where concentration gradients exist. The examination of polymerization dynamics benefits from the use of molecular rotors because of their real-time response rates. Presently, the reaction may force the reporters into specific areas of the polymer matrix, for example, into water pockets, but targeted molecular rotors that integrate with the matrix could prevent this behavior. With their relationship to free volume, the field of fluid dynamics can benefit from molecular rotors, because the applicability of viscosity models (DSE, Gierer-Wirtz, free volume, and WLF models) can be elucidated. Lastly, an important field of development is the surface-immobilization of molecular rotors, which promises new solid-state sensors for microviscosity [145]. 

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