Surface optodes

Other inorganic polymers, such as silicones, have excellent optical and mechanical properties for optical membranes. A great number of easily handled commercial silicone prepolymers are available but they have some disadvantages towards other materials. The surface is not easily modifiable to covalently immobilize indicators, they are not suited to combine with the customarily used support structures, owing to hard adhesion, and they are bad solvents for most of the indicators. 

Their main characteristic is that the optically active reagents are immobilized over the surface of an optical component (waveguide, metallic plate, glass, prism, etc.) or in a porous matrix in a way that they are in direct contact with the analyte in the sample solution. This immobilization can be carried out by covalent bonding [29], by mechanical interactions such as physical adsorption [30], by physical entrapment or by electrostatic interactions [31]. 

The selective recognizing reactions take place only in the surface that is in contact with the solution. Then, the response time depends on the equi- 

---

As it is shown in Figure 8, the enzyme can be immobilized in the vicinity (membrane, beads, etc) or on the surface of the fiber for optical fiber sensor development. Alternatively, it can be placed in a reactor and use the optode... 

Luminescence core-based optodes have been reported as waveguide capillary flow cells in liquid-filled optical fibers [ 103] or with polymers attached to the inner surface of a glass capillary [104],... 

Glud, R. N., Wenzhofer, F., Tengberg, a., Middelboe, M., Oguri, K. Kitazato, H. 2005. Distribution of oxygen in surface sediments from central Sagami Bay, Japan In situ measurements by microelectrodes and planar optodes. Deep-Sea Research I, 52, 1974-1987. 

Many patents have been issued for pH optodes, both for absorption and reflectance measurements [11,15-17] and for fluorescence [18-22]. The interaction of a pH-sensitive layer deposited as cladding on the surface of a Hber has also been proposed [23]. Figure 17-3 shows a number of arrangements developed in various laboratories. 

Along with simple optical sensors that measure transmission, so-called optodes [169] play an important role. In these, either the color change of an indicator dye in a membrane is monitored by using diffuse reflection [170], or the effect of an analyte on the fluorescence spectrum is observed. In addition. many other effects are used, such as surface... 

---