Optical sensors/optodes

Morf W.E., Seiler K., Lehmann B., Behringer C., Hartman K., Simon W., Carriers for chemical sensors design features of optical sensors (optodes) based on selective chromoionophores, Pure Appl. Chem. 1989 61 1613. 

Both organic and inorganic polymer materials have been used as solid supports of indicator dyes in the development of optical sensors for (bio)chemical species. It is known that the choice of solid support and immobilization procedure have significant effects on the performance of the optical sensors (optodes) in terms of selectivity, sensitivity, dynamic range, calibration, response time and (photo)stability. Immobilization of dyes is, therefore, an essential step in the fabrication of many optical chemical sensors and biosensors. Typically, the indicator molecules have been immobilized in polymer matrices (films or beads) via adsorption, entrapment, ion exchange or covalent binding procedures. 

Earlier, the electrochemical detections were mostly employed in chemical sensors and biosensors, and until now they are most commonly used, especially in commercially available sensors, mainly for clinical and environmental analyses. An intensive development of optical sensors (optodes) in recent 30 years has resulted in numerous designs and commercial products, which are increasingly competitive to electrochemical sensors. A more limited importance, especially as mass production is concerned and applications in routine analyses, have thermal and mass-sensitive sensors and biosensors. 

Opitz, N., Lubbers, D. W., Electrochromic Dyes, Enzyme Reactions and Hormone-Protein Interactions in Fluorescence Optic Sensor (Optode) Technology , Thlanta 35 (1988) 123-128. 

SP (Vis) The redox indicatoi ferroin, tris(l,10-phenanthroline)Fe(II) is incorporated into the perfluorosulfonated cation exchange membrane Nafion and, together with optical fibers, a photodiode, and a light-emitting diode, is used for the construction of a redox optical sensor (optode)... 

The optode transduces the non-optical signal from the environment to the optical one, readable by the photodetector. Various indirect optical sensors and theirs applications are described in literature35. The optode can work as a chemical sensor that detects certain analytes in aqueous solutions or in air on chemical way. It means that changes in the environment cause the changes in the photosensitive material, which is immobilized in the optode matrix. These chemical changes influence the observed light intensity (for example, due to absorption) or one can analyze the intensity or time decay of luminescence. There are numbers of publications devoted to the family of optical chemical sensors36. 

Construction of the optode for optical biosensor requires immobilization of sensitive compounds in the host matrix. There are several methods enabling molecules entrapment. One can use gels, polymers, saccharose, various meshes and membranes78. In case of fiberoptic indirect sensors optode must be attached to the fiber tip. Nowadays, there are two commonly used optode host materials sol-gel materials and polymers. 

Ion-selective electrodes are now well understood in terms of the underlying theory, and this has made it possible for new sensing principles to emerge that make use of the thousands of chemical receptors originally developed for ion-selective electrodes. One is the field of optical sensors, which has not been discussed here because it is outside the focus of this chapter. Such so-called bulk optodes do not require electrical connectivity between the sensing and detection unit and are therefore more easily brought into various shapes and sizes, including particle formats, which suit the need of modem chemical analysis. 

P. Buhlmann, E. Pretsch, and E. Bakker, Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors. Chem. Rev. 98, 1593-1687 (1998). 

From a general point of view, a chemical sensor is a device capable of continuously monitoring the concentration of an analyte. The two main classes are electrochemical sensors and optical chemical sensors. The latter are based on the measurement of changes in an optical quantity refractive index, light scattering, reflectance, absorbance, fluorescence, chemiluminescence, etc. For remote sensing, an optical fiber is used, and the optical sensor is then called an optode because of... 

We can create optical sensors for specific analytes by placing a chemically sensitive layer at the end of the fiber. An optical fiber sensor is called an optode (or opt rode), derived from the words "optical and "electrode. Optodes have been designed to respond to diverse analytes such as sulfites in food, nitric oxide in cells, and explosives in groundwater.12... 

Fig. 1 Chemical interaction mechanisms, basic components of the optical sensor instrumentation and their operation. Mechanisms direct measurement of chemical compounds that exhibit spectroscopic properties (1 A) and measurement of light originating from a chemical or a biological reaction in chemiluminescent or bioluminescent phenomena (IB) 2 optodes based on the interaction of indicators and labels with light, which are immobilized in a support and sensors that modify the intrinsic physical or chemical properties of a waveguide (refractive index, phase, etc.) as a result of the presence of the analyte (3A), a recognition element (35), an intermediate analyte (3C) or an indicator (3D)...

The IWAO proves to be a very promising alternative to the conventional optical sensors, as well as those based on optical fibers such as the conventional flow cell configuration. Fully reversible, reproducible, fast and sensitive bulk optodes are obtained. 

A more sophisticated class of optical sensors with high selectivity towards ions are the ion-selective optodes (ISOs) [21], where the matrix (hydrophobic polymer such as PVC) contains a selective lipophilic ionophore (optically silent), a chromoionophore, a plasticizer and an anionic additive. The measurement principle is based on a thermodynamic equilibrium that controls the ion exchange (for sensing cations) or ion coextraction (for sensing anions) with the sample. The source of optode selectivity is a preferential interaction between the target ion and an ionophore. For a dye to act as a chromoionophore, it must... 

NOj, cr, CIO4 VII. Ion Optodes (Ion-Selective Optical Sensors) polymer liquid membranes ... 

Ion Optodes The principles underlying the sophisticated complex polymer-based matrices for ISEs are the same as those used to design and construct ion-selective optical sensors, the optodes. Ion optodes have been developed for H, alkali metal ions, NH, Ca, NO, and CO . Numerous sensors for... 

Single-use devices for blood gas and other critical care measurements are also available through optical sensors or optodes (see Chapters 4 and 27). The Osmetech OPTI Critical Care Analyzer (Figure 12-8) and the Radiometer NPT 7 are examples of this type of technology. The advantages of optical systems compared with electrochemical transducers include the fact that they do not have to be calibrated to correct for electrode drift, and therefore the sensors are calibrated at the time of manufacture. ... 

H. Yanagi, T. Sakaki and T. Ogata, Development of high-performance ion sensors based on the functions of crown ethers and synthetic bilayer membranes, Nippon Kagaku Kaishi, 1999, 1999, 629 P. Izatt, E. Pretsch and E. Bakker, Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors, Chem. Rev., 1998, 98, 1593 S. Yajima and K. Kimura, Recent trends in ionsensing research, Bunseki Kagaku Anal. Chem.), 2000, 49, 279 etc. 

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