Which technique represents a single-diffusion reaction?

Which technique represents a single-diffusion reaction?

• A. Radial immunodiffusion
• B. Ouchterlony diffusion
• C. Immunoelectrophoresis
• D. Immunofixation electrophoresis

Answer: (A)

Single-diffusion assays involve only one reactant moving through a semisolid medium that contains the other, so a precipitate forms where they meet. Radial immunodiffusion fits this pattern: antigen diffuses outward from a well into an agar gel that already contains uniformly distributed antibody. As diffusion proceeds, they encounter each other and form a circular precipitin ring. The size of that ring reflects the antigen concentration, making this method useful for quantitative measurements. In contrast, techniques like Ouchterlony diffusion rely on both antigen and antibody diffusing in the gel, producing intersecting lines from two moving components. Immunoelectrophoresis adds electrophoretic separation before diffusion, and immunofixation electrophoresis combines separation with immobilized reactions and fixation steps. These involve multiple moving species or sequential steps, not a single-diffusion setup.

Single-diffusion assays involve only one reactant moving through a semisolid medium that contains the other, so a precipitate forms where they meet. Radial immunodiffusion fits this pattern: antigen diffuses outward from a well into an agar gel that already contains uniformly distributed antibody. As diffusion proceeds, they encounter each other and form a circular precipitin ring. The size of that ring reflects the antigen concentration, making this method useful for quantitative measurements.

In contrast, techniques like Ouchterlony diffusion rely on both antigen and antibody diffusing in the gel, producing intersecting lines from two moving components. Immunoelectrophoresis adds electrophoretic separation before diffusion, and immunofixation electrophoresis combines separation with immobilized reactions and fixation steps. These involve multiple moving species or sequential steps, not a single-diffusion setup.