Determination of Total Bile Acids in Serum by Enzymatic Electrochemiluminescence

Bile acids are dehydrogenated to 3-oxo bile acids by 3 alpha-hydroxysteroid dehydrogenase(3 alpha-HSD) with concomitant reduction of nicotinamide adenine dinucleotide (NAD+) to reduced nicotinamide adenine dinucleotide(NADH), which could enhance the electrochemiluminescence intensity of tris (2,2'-bipyridine) ruthenium (1)(Ru(bpy)(3)(2+)). Based on the principle above mentioned, bile acids could be detected by electrochemiluminescence method indirectly. The detection cell was filled with 2.5 mmol/L Ru(bpy)(3)(2+), 833 U/L 3 alpha-HSD, 70 nmol/L NAD(+) and 50 mmol/L phosphate buffer saline(pH 8.0). The ECL intensity was linear with the concentration of bile acids in the range from 1.0 fmol/L to 100 fmol/L and the linear equation was y = 0.7707x + 12.04 (r = 0.9975). The detection limit was 0.02 fmol/L and the average recovery was 97.5%. The ECL method established in this experiment was closely related to the enzymatic cycle method in clinical analysis.