The preparation and performance of two enzymebased fiber-optic sensors (optrodes) capable of detecting penicillin are described. Each sensor consists of a polymer membrane that is covalently attached to the tip of a glass optical fiber. The membrane contains the enzyme peniclilnase and a pHsensitive fluorescent dye. A signal Is produced when the enzyme catalyzes the cleavage of the &lactam ring of penicillin to produce penicilloic acid and, consequently, a pH change in the microenvironmmt of the membrane. The sensors differ in the way the polymer membrane is constructed and in the type of pH indicator dye used. Both optrodes exhibit response times (40-60 8 ) significantly lower than those of the corresponding enzyme electrodes (2 min). Each gives a linear response over the concentration range of 0.000 25 to 0.01 M penicillin 0, when measured in a 0.005 M phosphate butler. The data indicate that these ImmoMilzation strategies produce similar results and may be considered complementary alternatives in future enzyme optrode appiications.
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