Autoclavable Optical Oxygen Sensors: Instrumentation, Polymer Matrices and Results
Publication from Health
Voraberger H., Kern W., Kreimaier H., Bierbernik K., Kolle C., Beneš R., Trettnak W., Gruber W., Reininger F.
N?¬?rnberg (Germany) Proceedings on the 9th Int¬¨¬•l Trade Fair and Conference for Sensors, Transducers & Systems (Sensor 99), 1999
Autoclavable Optical Oxygen Sensors: Instrumentation, Polymer Matrices and Results 1 Institute for Chemical Technology of Organic Materials, Stremayrgasse 16/II, 8010 Graz, Austria, tel. 0043-316-873-8457, fax 0043-316-873-8951 2 Joanneum Research, Institute for Chemical and Optical Sensors, Steyrergasse 17, 8010 Graz, Austria, tel. 0043-316-876-1226, fax 0043-316-876-1230 Polymers, which are used in optical sensors as the carrier of the dye, have to meet many physical and chemical characteristics. In particular, if they should be steam sterilized (e. g. they have to stay transparent, be resistant against light and oxidation, have a high glass transition temperature, etc.). In our work we have chosen some polymers with promising literature data and investigated their behavior under the conditions of steam sterilization. First the neat polymers were investigated to figure out their behavior under these harsh conditions. To characterize changes in the polymer matrix we used IR-spectroscopy (to detect changes caused by oxidation), GPC (for changes in the molecular weight), a light and an electron microscope (for mechanical changes). It turned out that some polymer films are not suitable for autoclavation. One of them was polyvinylnaphthalene, which was prospected to have similar characteristics as polystyrene but a higher glass transition temperature. However after steam sterilization the polyvinylnaphthalene film was milky and dull and therefore unsuitable for an optical sensor. Fig. 1 shows an electron micrograph of polyvinylnaphthalene after steam sterilization. Bubbles and changes of the surface are responsible for the clouding of the polymer film. Polysulfon and Polyetherimide remain unchanged under sterilization conditiones. It turned out that it is necessary to pretreat the oxygen sensors (i.e. polymer and dye) to obtain reliable and reproducable measurements. By this thermal pretreatment the remaining solvent and water is removed and stress is reduced. To investigate this we established Stern-Volmer-Plots of these sensors pretreated under different conditions. It proved useful to dry the sensors in the drying oven at 140°C for 12 hours (fig.2). Plot were made before and after autoclavation. If the polymer is pretreated under these conditions there is nearly no difference between the Stern-Volmer-Plot before and after steam sterilization. Finally we want to show the first results we obtained with the sensors under working conditiones. They were used in bioreactors to measure the oxygen consumption. These new optical oxygen sensors were compared to the conventionally used electrochemical sensors. With both sensor types similar results were obtained. Therefore polymer based optical oxygen sensors are a good alternative to electrochemical sensors
Additional informations: 18-20 May 1999, Vol. 2: S. 571-576