Sk. Spear et al., Ammonia measurements in mammalian cell culture media with a diffuse reflectance-based fiberoptic ammonia sensor, APPL BIOC B, 75(2-3), 1998, pp. 175-186
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.