Sandwich-type assays

Sandwich-Type Assay Based on Biotinylation of a Target Hapten. 145... 

The assay procedures described in this section include chemical derivatization of a target hapten molecule to enable a variation of the sandwich-type assay. 

Figure 2. Right Microtiter-based TSH bioluminescent immunoassay. Left The schemes of the TSH sandwich-type assay (1), TT4 (2), and FT4 (3) competitive assays.

Briefly, the sandwich type assay consists in the incubation of streptavidin-coupled-MB with an antihuman IgG biotin conjugate, and then, the immunological reaction with the human IgG antigen takes place. After that, a gold labeled anti-human IgG reacts with the antigen, and finally the AuNPs are elec-trochemically detected. 

Fig. 2. Schematic (not in scale) of (a) AuNP conjugation with anti-human IgG (b) analytical procedure for the sandwich type assay and the electrochemical detection.

Fig. 3. Transmission electron micrographs (TEM) images of the MB after the sandwich type assay, carried out with a nonspecific antigen (goat IgG) (blank assay-(A)) and with 1.0x10-3 pg/mL of human IgG (B).

Principles and characteristics of lateral flow strip assays are reviewed. Recent technology developments permit the use of inexpensive electronic readers for interrogating lateral flow strip test results, thus avoiding the inevitable variation and subjectivity of visual inspection to assess the capture of reporter-labeled analyte on test lines of the strip. Protocols for developing lateral flow assays are described, including two specific case studies for assaying cotinine (a small-molecule metabolite of nicotine) in a competitive format, and assaying HIV antibodies in a sandwich-type assay format. 

Figure 9.8. Steps of the sandwich-type assay (1] The redox polymer and the oligonucleotide probe are electrodeposited on the screen-printed electrode (SPE) [2] the capture probe and the target are hybridized (3] the electrode-bound target and the HRP-labeled oligonucleotide are hybridized, the HRP labels are in electrical contact with the redox polymer and (4] the electrocatal5dic reduction current of H2O2 to water is measured. Reprinted with permission from ACS [38].

Figure 21 Schauatic representation of labeling DNA assay, (a) Direct label assay, (b) Sandwich-type assay.

The SERS intensities for standard colloids or often quite weak, but can be easily enhanced by binding a strong chromophore near the surface of a metal cluster. Such labeled metal-clusters are adsorbed to a metal chip surface, preferably in a sandwich type assay. With a protein having a strong chromophore itself it can act as the label and analyte at the same time, binding the colloidal particle to the SERS active surface. In an ideal setup the protein is then sandwiched between two SERS active clusters. If the... 

Nanoparticles can also act as labels by serving as catalysts for electrochemical reactions. For example, PtNPs have been employed in electrochemical biosensors due to their ability to catalyze the reduction of hydrogen peroxide. Picomolar DLs for DNA and nanomolar DLs for thrombin were demonstrated using electrochemical hybridization and sandwich-type assays that employed PtNP labels for this purpose. ... 

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