Which of the following characteristics describes a capture or sandwich enzyme assay?

Which of the following characteristics describes a capture or sandwich enzyme assay?

• A. Less sensitive than competitive enzyme assays
• B. Requires two wash steps
• C. Best for small antigens with a single determinant
• D. A limited number of antibody sites on solid phase

Answer: (B)

In a capture or sandwich enzyme assay, the antigen is captured between two antibodies: a capture antibody anchored to a solid surface and a second detection antibody that binds a different epitope on the antigen. Because two binding events occur, thorough washing is essential to remove unbound components after each step and to reduce background, so the signal truly reflects the specific antigen–antibody sandwich that has formed. This makes two wash steps a defining operational feature of the method. As a result, this format is typically more sensitive than competitive assays, since the sandwich requires two specific bindings and can produce a stronger, cleaner signal. It also relies on the antigen having at least two distinct epitopes for the two antibodies to recognize; thus it isn’t ideal for very small antigens with a single determinant. The number of antibody sites on the solid phase isn’t a defining trait of the sandwich approach.

In a capture or sandwich enzyme assay, the antigen is captured between two antibodies: a capture antibody anchored to a solid surface and a second detection antibody that binds a different epitope on the antigen. Because two binding events occur, thorough washing is essential to remove unbound components after each step and to reduce background, so the signal truly reflects the specific antigen–antibody sandwich that has formed. This makes two wash steps a defining operational feature of the method.

As a result, this format is typically more sensitive than competitive assays, since the sandwich requires two specific bindings and can produce a stronger, cleaner signal. It also relies on the antigen having at least two distinct epitopes for the two antibodies to recognize; thus it isn’t ideal for very small antigens with a single determinant. The number of antibody sites on the solid phase isn’t a defining trait of the sandwich approach.