Capillary enzyme immunoassay with electrochemical detection for determining indole-3-acetic acid in tomato embryos

An amperometric immunoassay for indole-3-acetic acid (IAA) in tomato embryos was developed. The antibody against IAA was covalently bound to the chemically modified inner surface of a 22 μL silica capillary. The competitive binding of methylated IAA and an IAA alkaline phosphatase conjugate for a limited amount of antibody was accomplished in the silica capillary in 20 min. The enzymatic product p-aminophenol, produced from p-aminophenyl phosphate, was determined by flow injection analysis with amperometric detection. A detection limit for IAA of 3 pg/μL was obtained. The average concentration of IAA in mature embryos measured by this method is 0.37 ± 0.03 μg/g. Although isotope dilution GC-SIM-MS can achieve the same detection limit, the sample analysis is not feasible in such a complicated matrix and further purification and separation are required.