Final answer:
In biochemical and analytical chemistry, heterogeneous assays such as ELISA and Western blot require a physical separation step before analyte detection. ELISA employs antibodies and enzyme-linked reactions to visualize antigens, while Western blot uses antibodies to detect proteins after gel electrophoresis. PCR, however, is not a heterogeneous assay.
Step-by-step explanation:
Examples of heterogeneous assays used in biochemical and analytical chemistry include enzyme-linked immunosorbent assay (ELISA), Western blot, and flow cytometry. These assays are termed heterogeneous because they require a separation step before the detection of the analyte.
In the case of ELISA, antigens are immobilized on a microtiter plate and detected using an enzyme-conjugated antibody specific for the antigen. A substrate is then added, which is converted into a colored end product in the presence of the enzyme, indicating the presence of the antigen. The direct ELISA is a variation of this assay where the detecting antibody is directly conjugated to an enzyme, which, though faster, may have lower sensitivity compared to other ELISA variations.
Western blot follows protein separation through gel electrophoresis. Proteins are then transferred to a membrane and probed with antibodies specific to the protein of interest. Secondary antibodies, often linked to enzymes or fluorophores, provide the means of visualizing the proteins.
Lastly, PCR is not a heterogeneous assay and therefore does not belong in this list, as it is a nucleic acid amplification technique with no inherent requirement for a separation step before detection