Detection using avidin-biotin interactions

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). 

After sulfo-NHS-SS-biotin-modified molecules are allowed to interact with avidin or streptavidin probes, the formed complexes can be cleaved at the disulfide bridge by treatment with 50 mM DTT. Reduction releases the biotinylated component from the avidin or streptavidin detection reagent. The use of disulfide biotinylation reagents thus provides much gentler conditions to break the complex than would be required if the avidin-biotin interaction itself were disrupted (which dissociates only at 6—8 M guanidine, pH 1.5). 

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). 

Large differences between the interfacial properties of ds and ssDNAs observed earlier by capacitance measurements [10, 37] suggested that a.c. impedance measurements could be used to detect DNA hybridization on electrodes [433, 434] (Sect. 12.8.). A three-component ODN system on a gold electrode (involving avidin-biotin interactions) was used to detect specific DNA sequences by means of faradaic impedance spectroscopy [435]. Impedance spectroscopy does not seem, however, to be the most convenient method for the DNA biosensor faster and simpler voltam-metric or chronopotentiometric methods will probably be more convenient. Gon-ductivity of the perfect DNA, contrasting with a loss of conductivity in duplexes with mismatched bases, may be of use in... 

Saleh et al. [66] used a similar approach. Direct binding of avidin to biotin was optically detected by using (1) UCNPs that carry avidin on their surface and (2) biotinylated gold nanoparticles. The spectral overlap between the green upconversion emission and the absorption of the red gold nanoparticles results in a quenching of the UCNP fluorescence upon avidin-biotin interaction (Fig. 13b). 

Biotinylated oligosaccharides are convenient probes of carbohydrate interactions, because the biotin label can be captured or detected using an avidin or streptavidin derivative. For instance, immobilized streptavidin can be used to purify glycoconjugates that have been labeled... 

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