Ammonia measurements in mammalian cell culture media with a diffuse reflectance-based fiberoptic ammonia sensor

A solid-state, diffuse reflectance-based fiberoptic sensor is described for quantifying ammonia. This sensor is constructed by immobilizing chlorophen ol red, a weak acid chromophoric indicator dye, in a microporous polypropyl ene membrane. A flow-injection analysis system is used to carry a 10-mu L a liquot of the sample across the treated membrane. Ammonia in the sample dif fuses through the air-filled pores within the membrane structure before rea cting with the indicator dye. A reversible acid-base reaction between ammon ia and chlorophenol red results in a measurable change in the reflectance a t 560 nm. Response characteristics include a peak response within 20 s, a l imit of detection of 0.2 +/- 0.1 mid ammonia, and a dynamic range of up to 60 mM ammonia. The analytical utility of this sensor is demonstrated by mea suring ammonia levels in 48 individual samples collected during the growth of PC3 human prostate cancer cells in a typical serum-containing growth med ium. Accuracy of the proposed sensor is verified by a comparison of results from this sensor to those from a conventional enzyme assay.