Streptavidin liposomes

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin—avidin or biotin—streptavidin complexes. The avidin— biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 13) (Savage et al., 1992). 

FIGURE 7.38. Computer generated model of a liposome-streptavidin conjugate (a), a schematic representation of a liposome-streptavidin (Sav)-concanavalin A (Con A)-streptavidin multilayer (b) and of streptavidin crosslinked vesicles (c). 

Fig. 2. A Interaction of biotin with the tetrameric protein streptavidin. B Schematic representation of the aggregation of biotinylated liposomes induced by the tetrameric streptavidin protein (taken from [16])...

An avidin-biotin system has been used to attach antibodies in the bilayer of DDSs. Xiao et al. developed a three-step strategy to improve the tumor-to-tissue ratio of anticancer agents [184], Two antibodies specific for the CA-125 antigen that is highly expressed on NIH OVCAR-3 cells were used. These cells were prelabeled with biotinylated anti-CA-125 antibody and fluoroscein isothiocyanate (FITC)-labeled streptavidin (SAv) prior to administration of biotinylated liposomes. Both antibodies were specifically bound to the cell surface of OVCAR-3 cells but not to SK-OV-3 cells, which do not express the specific antibody. Antibody biotinylation did not affect its immunoreactivity. 

Linkage of enzyme and antibody by auxiliary molecules provides a potentially universal and variable number of systems for use in bioassays. The most common linkage system involves the recognition of biotin by avidin, or more commonly streptavidin (due to its higher affinity for biotin), although the use of staphylococcal protein A can be used for some antibody isotypes (11). An alternative system, but one that is not often used, involves liposomes loaded with enzyme that has antibody molecules on its surface (49). 

Fig. 5. Sandwich-hybridization assay (A) A biotinylated DNA oligonucleotide, which is complementary to one portion of the target sequence, is mixed with streptavidin and applied to form the capture zone 1.5 cm from the base of the membrane. An unmodified DNA oligonucleotide, which is complementary to the reporter probe sequence on the liposomes, is applied to form the control zone 2.5cm from the base of the membrane. (B) In the presence of target, a sandwich hybridization complex forms with dye-encapsulating liposomes resulting in a magenta-colored band at the capture zone. (C) In the absence of target, only the control band is visible as no sandwich complex has formed.

Fig. 2 In situ AFM images (left) and line scans (right) of biotinylated vesicles with a nominal diameter of 100 nm attached to a streptavidin monolayer, a A low biotin content (2 mol %) results in the adsorption of intact liposomes within the timescale of observation (about Ih) b a high biotin content (30mol%) yields planar lipid bUayers exhibiting a typical height of 5-6 nm...

A traceless detection of Escherichia coli has been reported by Ahn and co-workers (Figure 10.2). Two polymerizable lipids (one containing biotin. Figure 10.2) and DMPC were used to form the liposomes. The liposomes were spotted on streptavidin... 

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