Surfaces, biotin-streptavidin

Covalent attachment of enzymes to surfaces is often intuitively perceived as being more reliable than direct adsorption, but multisite physical interactions can in fact yield a comparably strong and stable union, as demonstrated by several biological examples. The biotin/streptavidin interaction requires a force of about 0.3 nN to be severed [Lee et al., 2007], and protein/protein interactions typically require 0.1 nN to break, but values over 1 nN have also been reported [Weisel et al., 2003]. These forces are comparable to those required to mpture weaker chemical bonds such as the gold-thiolate bond (1 nN for an alkanethiol, and even only 0.3 nN for a 1,3-aUcanedithiol [Langry et al., 2005]) and the poly(His)-Ni(NTA) bond (0.24 nN, [Levy and Maaloum, 2005]). 

D protein arrays based on biotin-streptavidin architectures are likely to be the system of choice due to their ease in handling, excellent signal-to-noise ratio and non-specific interactions. 3D surfaces based on porous gold, sol-gel materials, polymer brushes and dextran surfaces are widely used to mimic the properties of bulk solution and increase the immobilization capacity of proteins. 

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 26. Schematic of the post hybridization detection method. A DNA target solution labeled with biotin is first incubated with the DNA probe functionalized chip. Targets diffuse passively from the solution to the surface where they hybridized with the probes if complementary. A solution containing streptavidin-functionalized magnetic labels is then incubated with the chip. Labels bind through the biotin-streptavidin interaction to where hybridization occurred. DNA hybridization is detected with spintronic transducers.

The library is allowed to react with biotinylated target in solution, usually a MAB, then added to a streptavidin-coated Petri dish. Phages displaying peptides binding to the antibody are adsorbed to the plastic surface through biotin-streptavidin bonds. 

Our own experiments focused on creating biotin-streptavidin coated microwells as biochemical reaction vessels (Fig. 9). The wells were used to prevent evaporation of reaction components, a problem that plagued similar experiments done on flat surfaces. The microwells were chemically etched used conventional silicon etching techniques (Fig. 9a). The same mask used to create the microwells was used to direct the linkage of photoactivatable biotin to the well surfaces (Fig. 9b). Then, the chip was flooded with protein to create a floating streptavidin surface (Fig. 9c). These chips were used in rolling circle... 

To demonstrate MT-MEC as a useful platform for protein quantification, a simple surface biotin-avidin assay was constructed[15,16]. In the assay, biotinylated-BSA is incubated on both silvered and glass substrates (Figure 15.5). HRP-streptavidin is then added to the surface, locaiizing the enzyme catalyst in close proximity to the silver for MT-MEC. The peroxide and Acridan (iumophore) are then added to initiate the chemiluminescence reaction. While this assay in essence determines BSA concentration, this model assay could indeed be fashioned to both iocaiize and sense other proteins / DNAs of interest. 

Fig. 4.6. Image of individual ss DNA fragments labeled at the 5 end with a tetramethyl Rhodamin molecule and positioned at the surface of a cover glass by biotin-streptavidin [23]...

A DNA optical sensor system was proposed by Cass and co-workers [35] based on the combination of sandwich solution hybridization, magnetic bead capture, flow injection and chemiluminescence for the rapid detection of DNA hybridization. Sandwich solution hybridization uses two sets of DNA probes, one labelled with biotin, the other with an enzyme marker and hybridization is performed in solution where the mobility is greater and the hybridization process is faster, rather than on a surface. The hybrids were bound to the streptavidin-coated magnetic beads through biotin-streptavidin binding reaction. A chemiluminescence fibre-optic biosensor for the detection of hybridization of horseradish peroxidase-labelled complementary DNA to covalent immobilized DNA probes was developed by Zhou and co-workers [36]. 

Antibodies or other binding proteins (e.g., protein A, biotin-avidin, and biotin-streptavidin) adsorbed or covalently attached to an insoluble matrix (e.g., plastic beads, inside surface of a plastic tube or microwell, and magnetic beads)... 

Whatever the coupling agent is, the control of non-specific protein absorption is important to the use of nanomaterials in specific protein binding. There are plenty of molecules used for protection of various surfaces from proteins with mechanisms as steric repulsion, hydration and solvent structuring. For example, the modification of CNTs with the absorption of biotinylated Tween 20 allowed streptavidin recognition by the specific biotin-streptavidin interaction, but provided resistance towards other protein absorption [133]. 

---