Immunoassay systems based on immunoliposomes consisting of genetically engineered single-chain antibody

The single-chain antibody against 2-phenyloxazolone was modified with lipid molecules at its amino-terminus by genetic engineering. The engineered lip id-tagged antibody molecules were incorporated into liposomes consisting of phosphatidylcholine, and the immunoassay systems were constructed by the r esulting immunoliposomes. One immunoassay system was based on fluoroimmunoa ssay. A competitive fluoroimmunoassay for caproic acid conjugate of 2-pheny loxazolone as a model antigen was performed with the carboxyfluoresceine-en capsulated immunoliposomes. Antigen could be determined in the concentratio n range from 10(-7) to 10(-9) M. The other system was based on quartz cryst al microbalance (QCM). The immunoliposomes were competitively reacted with analyte to the hapten-immobilized surface of a crystal plate. The frequency change was observed by injection of the mixture of the immunoliposomes and analyte in a concentration dependent manner. In this competitive QCM assay , antigen could be measured in the concentration range from 10(-5) to 10(-8 ) M. Furthermore, direct observation of the immunoliposomes on the hapten-c oated solid-surface by atomic force microscopy (AFM) was also performed in this study. (C) 2000 Elsevier Science S.A. All rights reserved.