Determination of ammonia in untreated serum with a fiber-optic ammonia gas ensor

A fluorescence-type fiber-optic ammonia gas sensor has been developed for the determination of ammonia in untreated serum. An internal solution has been designed to provide both the selectivity and limit of detection required for this measurement. Selectivity over carbon dioxide is accomplished by adjusting the level of ammonium chloride in the internal solution. A sub-micromolar detection limit is obtained by using a combination of 2′,7′-dichlorofluorescein and 5-carboxy-2′,7′-dichlorofluorescein as the indicator dyes. The limit of detection for the resulting sensor is 0.09 μM and response times range from 2 to 6 min. When applied to the determination of ammonia in eighteen untreated serum samples, the results from the sensor compare favorably with those from the conventional glutamate dehydrogenase assay.