Correct Option: B

Required for the sandwich assay, the capture antibody binds to the antigen of interest and generates a detectable signal for quantification. This antibody is usually polyclonal in nature, and is conjugated with an enzyme (most commonly, horseradish peroxidase), so that, upon substrate addition, a colored product is formed. The density of the color can then be measured spectropho-tometrically as a function of antigen concentration. The western blot (sometimes called the protein immunoblot) is a widely accepted analytical technique used to detect specific proteins in the given sample of tissue homogenate or extract. It uses gel electrophoresis to separate native proteins by 3-D structure or denatured proteins by the length of the polypeptide. The proteins are then transferred to a membrane (typically nitrocellulose or PVDF), where they are stained with antibodies specific to the target protein.