Fiber-optic chemical sensors and biosensors.

This biannual review covers the time period from January 2002 to January 2004 and is written in continuation of previous reviews (A1, A2). An electronic search in SciFinder and MedLine resulted in 532 hits. Since the number of citations in this review is limited, a stringent selection had to be made. Priority was given to fiberoptic sensors (FOS) for defined chemical, environmental, and biochemical significance and to new schemes and materials. The review does not include (a) FOS that obviously have been rediscovered; (b) FOS for nonchemical species such as temperature, current and voltage, stress, strain, and displacement, for structural integrity (e.g., of constructions), liquid level, and radiation; and (c) FOS for monitoring purely technical processes such as injection molding, extrusion, or oil drilling, even though these are important applications of optical fiber technology. Fiber optics serve analytical sciences in several ways. First, they enable optical spectroscopy to be performed on sites inaccessible to conventional spectroscopy, over large distances, or even on several spots along the fiber. Second, fiber optics, in being waveguides, enable less common methods of interrogation, in particular evanescent wave spectroscopy. Fibers are available now with transmissions over a wide spectral range. Major fields of applications are in medical and chemical analysis, molecular biotechnology, marine and environmental analysis, industrial production monitoring and bioprocess control, and the automotive industry. Note: In this article, sensing refers to a continuous process, while probing refers to single-shot testing. FOS are based on either direct or indirect (indicator-based) sensing schemes. In the first, the intrinsic optical properties of the analyte are measured, for example its refractive index, absorption, or emission. In the second, the color or fluorescence of an immobilized indicator, label, or any other optically detectable bioprobe is monitored. Active current areas of research include advanced methods of interrogation such as time-resolved or spatially resolved spectroscopy, evanescent wave and laser-assisted spectroscopy, surface plasmon resonance, and multidimensional data acquisition. In recent years, fiber bundles also have been employed for purposes of imaging, for biosensor arrays (along with encoding), or as arrays of nonspecific sensors whose individual signals may be processed via artificial neural networks. This review is divided into sections on books and reviews (A), specific sensors for gases and vapors (B), ions and salinity (C), miscellaneous inorganic and organic chemical species (D), and biosensors (E), followed by sections on application-oriented sensor types (F), new sensing schemes (G), and new sensor materials (H), respectively.