TABLE OF CONTENTS Optical techniques for chemical and biological analysis are well established. In many cases, sensors based on these techniques use optical fiber technology, although planar waveguide configurations are increasingly favored. Optical sensor devices can be used for the detection and determination of physical or chemical parameters through the measurement of changes in some optical property. There is increasing flexibility in the measurement mode, e.g. evanescent wave, surface reflectance, and emerging technologies such as surface plasmon resonance (SPR). There is also a drive towards integration of optical components (source, waveguides, sampling region, detectors) on a planar platform. The cost, power consumption and size of such components is rapidly decreasing with the result that there is the potential for low cost, multichannel information on absorbance, color, fluorescence and turbidity etc. Portable UV-Vis, Raman and fluorescence instruments are now available for field measurements.
Most optical sensors are based on a spectroscopic technique such as measurement of absorbance, reflectance or fluorescence, where the signal obtained is related to the concentration of the analyte. The two most popular methods are absorption and fluorescence. If both modes of detection are available for a particular compound, fluorescence would be preferable because of better sensitivity due to being measured against an almost zero background. It is also worth noting that a fluorescence signal is emitted by the molecules themselves (or reagent molecules) and therefore contains information about the molecule being measured, while absorption is based on the transmitted light left over after...
