Optical-fibre sensors by silylation techniques

Abstract

The detection of chemical parameters by means of optical fibres has had a decisive boost in recent years; the realization of these devices is related to the development of a great number of techniques. The former are characterized by a reagent fixed to an optical fibre, a procedure which is not in itself unique. The silylation technique is one of the most widely used for optrode realization. It generally involves an organosilicon compound that reacts with an external support or directly on the surface of the fibres with one or more functional groups and gives the supports a new functionality. Obviously the activation of the surface must be followed by other appropriate reactions so as to be able to immobilize the optically sensitive reagent. Silylation can be performed either on external glass or quartz supports or directly on the fibre itself. From a chemical point of view, there is not a big difference on where the chemical reaction takes place, but the same cannot be stated from the optical point of view. By changing where the silylation is performed, it is possible to change the optical path and consequently the signal-to-noise ratio, which is strictly related to the performance of the sensor. In fact, if the optical-fibre sensor is to be launched on the market, it must be competitive, in terms of cost and performance, when compared with other instruments that measure the same chemical species. Some of the most significant silylated optrodes are reported here, together with the associated optoelectronic instrumentation. Moreover, the advantages and drawbacks of the different procedures are taken into account.