Fiber Optic Chemical Sensors and Biosensors: a View Back

The past 30 years have seen enormous progress in opto-electronics, information technology and biotechnology, and fiber optic chemical sensors (FOCS) as well as fiber optic biosensors (FOBS) are one of the outcomes. Chemical sensors have been defined as follows 1 : Chemical sensors are miniaturized analytical devices that can deliver real-time and on-line information on the presence of specific compounds or ions in complex samples. In the easiest and simplest case, a sensor probe is inserted into the sample of interest to obtain an analytical signal that can be converted into a concentration unit. Chemical sensors ideally act fully reversibly, as do physical sensors for temperature, pressure, and the like. This has been achieved in few cases of FOCS only, and hardly in FOBS (except for some enzyme-based systems). However, despite the fact that most biosensors respond irreversibly or need to be regenerated, clinicians often refer to such single-shot detection elements as biosensors, provided a "reagent" or a "biology" is immobilized on a solid support. True sensors are expected to be small and to work even in complex samples, ideally without sample treatment. Both FOCS and FOBS rely on optical fiber waveguides which have become available in adequate quality in the late 1970s. In fact, they are so good now that sensing without intermittent amplification has become posssible over distances as large as 10 km. Clearly, this was only possible once the respective laser sources have become available.