Immobilization affinity directed

Figure 11 Schematic representation of techniques used for solubilized and immobilized affinity ligands in polyacrylamide gels. (A) Solubilized ligand method the ligand can move freely in the gel-buffer system. (B) Macroligand method the solution of acrylamide contains the macroligand that becomes entrapped within the gel matrix after polymerization. (C) Chemically bound ligand direct copolymerization of polyacrylamide gel with the copolymerizable derivative of the ligand. (Reproduced with permission from Ref. 13.)...

Li et al. developed a label-free capacitive immunosensor for rapid and sensitive detection of E. coll 0157 H7. The immunosensor was fabricated by immobilizing affinity-purified anti-C. coll 0157 H7 antibodies onto SAMs of 3-mercaptopropionic acid (MPA) on the surface of a quartz crystal Au electrode activated by immersion in EDC/NHS solution to convert the terminal carboxylic group of MPA to an active NHS ester. Bacteria suspended in solution became attached to the immobilized antibodies when the immunosensor was tested in liquid samples. The change in capacitance caused by the bacteria was directly measured and an equivalent circuit was introduced to simulate the capacitive itnmunosen-sor (Figure 14.1 la). This consisted of ohmic resistance (R ) of the electrolyte double-layer capacitance (C i) including and Cqq, electron-transfer resistance (Ret), and War-... 

In a direct immunoassay the immobilized antibody binds to the corresponding antigen. The competitive immunoassay relies upon the competition of the analyte with a labelled analyte for antibody binding. These formats are widely used for high throughput affinity arrays. A sandwich immunoassay is based on the trapping or capture of the analyte by another antibody. In ELISA (enzyme linked immunosorbent assays) the second antibody is conjugated with an enzyme. The bound enzyme labelled antibody is detected by its ability to break down its substrate to a colored product. 

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