CAPILLARY OPTICAL SENSORS

Glass or plastic tubings with a chemically sensitive coating on the inner surface are used for optical chemical sensing. Such devices possess several attractive features in that they (a) can act as a mechanical support for optically sensitive materials (coatings), (b) represent an optical waveguide structure and enable various methods of optical interrogation, (c) can serve as a sample cavity of well-defined volume, and (d) are suitable for direct sampling. The performance of such ''capillary optrodes'' is exemplified with a fast-responding and fully reversible carbon dioxide sensor chemistry. Its response time to gases (t(90)) varies from 100 to 300 ms. We also give arrangements for optical readout devices and show that capillary sensors can overcome some of the problems of optrode membranes mounted in flow cells or on fiber tips.