Liposome-based flow-injection immunoassay for determining theophylline in serum

We developed a method for quantitatively determining theophylline in serum, using a heterogeneous immunoassay called flow-injection immunoanalysis. The reaction involves competition between serum theophylline and theophylline-labeled liposomes. Separation occurs on a solid-phase reactor column containing immobilized antibody to theophylline incorporated in a flow-injection system. Subsequent lysis of the bound liposomes provides sensitive detection of the analyte. Effective regeneration of the immobilized antibody activity allows the reactor to be reused for hundreds of sequential samples. Comparison of the results of the flow-injection immunoassay method with results obtained with a commercially available fluorescence polarization method showed an excellent correlation.