Flow injection analysis using specific biochemical reaction on latex particles and liposome

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A New Flow injection method (FIA) was proposed in order to improve the reaction efficiency, in which enzyme was immobilized on the surface of synthetic polymer latex. Stirene-acrylic acid copolymer latex synthesized was spherical and had homogeneous size of about 0.5 mm diameter. The enzymatic activity of enzyme-immobilized latex was dependent on the molar fraction of acrylic acid. Lactate dehydrogenase immobilized on the latex particles kept the activity higher than 50% of original one for two months or longer. The results obtained in FIA using latex suspended in the carrier solution were comparable to those in the conventional FIA using enzyme-immobilized reactors. Difficulties in recovering and reusing the used latex were the serious problem.Another new FIA method (flow injection liposome immunoassay : FILIA) was discussed, in which antigen-immobilized liposome having marker molecules in its inner space was used and a competitive immunoassay was carried out in a continuous flow system. The sufficient activity of antibody immobilized on the wall of a reactor was confirmed by observing satisfactory results in a flow injection enzyme immunoassay using POD-conjugated antigen. However, any explicit proof for the immunoreaction could not be found in FILIA because of steric hindrance by bulky liposome and wide wall of the reactor. By inserting a hydrophillic polymer spacer between antigen and liposome or between antibody and the reactor wall, a sigmoid response was obtained for the free antigen injected as a sample. But the response was insufficient for the determination of low concentration of the free analyte.