Box 15-3 Protein Immunosensing by Ion-Selective Electrodes with Electrically Conductive Polymers

The electrode shown here has a gold wire coated with a thin layer of electrically conductive poly(3-octylthiophene). When the polymer is oxidized, electrons can move along the conjugated backbone of the molecule. 

An application of the Ag -electrode is in the sensitive detection of a protein by a sandwich irmnunoassay using antibodies. An antibody is a protein produced by the immune system of an animal in response to a foreign molecule, which is called an antigen. An antibody specifically recognizes and binds to the antigen that stimulated its synthesis. 

To complete the analysis, Ag metal is oxidized to Ag with hydrogen peroxide (H2O2) and the liberated Ag is measured by the ion-selective electrode. For 

50- ulL sample. An analogous assay of ribonucleic acid (RNA) with the Ag ion-selective electrode detects 0.2 amol (2 X 10 mol, 120 000 molecules) in a 4- xL sample. 

Sandwich immunoassay with deposition of silver metal on Au nanoparticles. [From K. Y. Chumbimuni-Torres, Z. Dai, N. Rubinova, Y. Xiang, E. Pretsch, J. Wang, and E. Bakker, y. Am. Chem. Soc. 2006,128,13676.] 

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Box 15-3 Protein Immunosensing by Ion-Selective Electrodes with Electrically Conductive Polymers... 

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