Sandwich assays, description

Figure 5.3 Detection of thrombin-aptamer interactions by electrochemical methods. (A) Sandwiched assay according to Ikebukuro et al. (2005). (B)-(D) Detection of thrombin using the electrochemical indicator methylene blue (MB). (See text for full description.) [(A) From Ikebukuro et al. (2005), with permission from Elsevier (B) from Hianik et al. (2005) (C) from Bang et al. (2005) (D) adapted from Xiao et al. (2005b), with permission from the American Chemical Society.]...

Figure 7.7 (A) AFM analysis of a porous anodic alumina (PAA) layer chip surface after Au deposition. (B) Detection of a sandwich-type binding assay between the aptamers and thrombin using Au-capped oxide nanostructures on the PAA layer chip. (C) Relative reflected intensity characteristics of (black line) a bare PAA layer chip, 10 p.M aptamer I immobilized on a gold-deposited PAA layer surface (red line), the binding reaction between 10 p.M aptamer I and 1 p.M thrombin on the chip surface (blue line), after the binding reaction between aptamer I/thrombin complex and aptamer II (green line). (See text for full description.)...

The number of components for the indirect sandwich ELISAs is increased and consequently, the number of reagent combinations. The reader should by now be familiar with the descriptions in diagrammatic form so that the next series of assays exploiting the indirect sandwich ELISAs can be examined more briefly, with the principles involved being highlighted. 

The terms competitive and sandwich of the two immunoassay types are descriptive of each assay procedure. In competitive inununoassay, an aliquot of enzyme-labeled antigen (Ag ) of known concentration is added to the sample for competitive binding to the primary antibody. Following this, the reaction surface is rinsed and the enzyme substrate (S) added. After allowing sufficient time for enzymatic conversion, the sample is analyzed for the electroactive enzyme product (P). The concentration of P bears an inverse relationship to the analyte (Ag) concentration because of the competitive binding of Ag. ... 

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