Simple Sensors That Work In Diverse Natural Environments: The Micro-Clark Sensor And Biosensor Family

In this review the developments made within the area of needle-shaped Clark-type gas sensors are summarized. Emphasis will be on design and functioning of the sensors, but examples of use in various environments are also included. Microscale Clark-type sensors have been constructed for O-2, N2O, NO, H2S and CO2. The tip diameters are often 10-70 mu m, but tip diameters can also be considerably larger, and O-2 and H2S sensors can be made with tips down to < 2 mu m. The excellent long term stability conferred by the enclosure of the electrochemistry behind a polymer membrane makes these sensors suited not only for very localized measurement including recording of concentration profiles, but also for long term environmental monitoring. The high level of stability and virtual absence of interferences make the gas microsensors ideal as transducers in biosensors. Biosensors for CH4, NOx- (i.e., NO3- + NO2-), NO2-, Volatile Fatty Acids (VFAs), Urea, and SO42- have thus been realized.