Biotin biomolecules with

FIGURE 133.2 Design of photocleavable biotin (PC Biotin) NHS reagents (a) water insoluble PC-Biotin NHS, (b) water soluble PC-Biotin NHS. After modification of biomolecule with PC Biotin and binding of the conjugate to streptavidin, light can be used to release the target biomolecule or reactivate it. 

Because of concerns about the safety of radioisotope use, researchers are developing fluorescent and chemiluminescent methods for detection of small amounts of biomolecules on gels. One attractive approach is to label biomolecules before analysis with the coenzyme biotin. Biotin forms a strong complex with enzyme-linked streptavidin. Some dynamic property of the enzyme is then measured to locate the biotin-labeled biomolecule on the gel. These new methods approach the sensitivity of methods involving radiolabeled molecules, and rapid advances are being made. 

The avidin-biotin immobilization method maintains the biological activity of the receptor molecules. Besides the biocompatibility of the procedure, the surface geometry of these films provides high accessibility of the immobilized biomolecules. In addition, the avidin molecules form a passivation layer on the transducer surface that prevents nonspecific adsorption of proteins on the surface. In contrast with conventional grafting or affinity binding, this step-by-step approach can also be applied to the preparation of assemblies containing multilayers of biological molecules [42],... 

An application of biomolecule-nanoparticle hybrid supramolecular assemblies is the sensitive detection of p53, a tumor suppressor protein, by AuNP streptavidin conjugates capped with multiple ferrocene molecules.26 As shown in Figure 8.6, a mixed monolayer of double-stranded DNA and 1-hexanethiol on an Au electrode is used to capture p53, which binds to DNA containing the consensus site sequence. Subsequent conjugation of the captured p53 with biotin allowed for attachment of... 

The use of gold nanoparticles as an electrochemical label for bionanalysis was introduced by Costa-Garcia and coworkers 62 Adsorptive voltammetry was used to detect the gold signal and monitor biotin-stieptavidin interactions on a pretreated carbon paste electrode with an adsorbed biotinylated albumin layer after immersion into a solution of streptavidin-coated colloidal gold. While colloidal gold had found widespread use as a histochemical label for biomolecules and an optical label based on absorption... 

The strong and specific biotin-streptavidin binding was used to assemble biomolecule-functionalized nanoparticles in multilayered structures.67 Application of an electrical field allowed the assembly of multilayer structures by using extremely low concentrations of nanoparticles with minimal nonspecific binding. A microelectrode array was used to facilitate the rapid parallel electrophoretic transport and binding of biotin- and streptavidin-functionalized fluorescent nanoparticles to specific sites. By controlling the current, voltage, and activation time at each nanoparticle adsorption step, the directed assembly of more than 50 layers of nanoparticles was accomplished within an hour. 

Whitesides and coworkers combined microfluidic networks with a PDMS platform to create patterned gradients of biomolecules on a surface.121 This method involves a two-step process (1) formation of a gradient of avidin within well-defined patterns by use of microfluidic channels and (2) specific interaction between the avidin gradient pattern and biotin. Such patterns with a density gradient of immobilized biomolecules may find application in studies on cell development and function. 

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