Liposome immunoassay, homogeneous

Canova-Davis, E., Redemann, C. T., Vollmer, Y. P., and Kung, V. T. (1986). Use of a reversed-phase evaporation vesicle formulation for a homogeneous liposome immunoassay. Clin. Chem. 32 1687-1691. 

Frost, S. J., Chakraborty, J., and Firth, G. B. (1996). Urinary microalbumin measurement using a homogeneous liposomal immunoassay. J. Immunol. Methods 194 105-111. 

Homogeneous liposome immunoassays using lytic agents other than complement and mellitin have also been used. Phospholipase C catalyzes the dephosphorylation of phospholipids, which in turn destabilizes the liposome. The assay is based on the inhibition of the lytic activity by an antibody binding to an antigen conjugated to phospholipase Gentamicin is analyzed by this method. 

When foreign cells enter the human body they are captured by antibodies, which attach themselves to the cell membrane surface. Complement binds to these antibodies in a specific order, after which the target cells are lysed. Because the liposome bilayer is structurally similar to the cell wall, complement can be used to completely lyse antibody-bound liposomes. Attention has to be paid to the fact that although complement is specific, some liposomes are susceptible to complement lysis, without being bound to an antibody. Most liposome immunoassays are homogeneous complement-based assays. 

Other homogeneous immunoassays Several further homogenous assay formats have been developed that capitalize on the ability of antigen-antibody complexes to form detectable clusters or networks. Examples include the latex particle agglutination assay and the latex particle agglutination inhibition assay, in which the analyte or the antibody is conjugated to latex beads, and the analyte is quantified by virtue of its ability to promote or disrupt agglutination. Another example is the liposome immunoassay, in which analyte molecules are coupled to lipids,... 

This method was developed by Collaborative Research Inc. (F3). The technique, based on the use of immunoreactive liposomes, may be classified as another type of homogeneous immunoassay. The liposomes are microscopic vesicles (200-1000 nm in diameter) consisting of a relatively impermeable lipid bilayer that delineates and separates an internal aqueous compartment from the external aqueous medium. The principle is as follows (Fig. 3 and Table 6). An enzyme, alkaline phosphatase, is encapsulated in the liposomes [E] and sequestered from the substrate, p-nitrophenyl phos-... 

Accommodation of a homogeneous separation-free immunoassay on a dry matrix. This is possible for SLFIA and for ARIS. Other possibilities are labeling with gold particles or liposomes. The art lies in contact-free accommodation of all the reagents on the test strip, in such a way that no immune reaction takes place during storage. 

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