Question

Fluorescent polarization immunoassays

		demonstrates a positive response as a depolarization of light
		Does not use Ab as part of the procedure
		demonstrates a depolarization of light in a negative response
		None of the above

Answer 1

demonstrates a depolarization of light in a negative response

Explanation: Fluorescent polarization immunoassays detect the presence of antigen (Ag) or antibody (Ab) in the sample. In this assay, either Ag or Ab will be attached to the surface. E.g. Let us consider Ab is attached with the surface (stationary) and you want to determine the presence of Ag in the sample. Antigen, attached to the fluorescent molecule, will be added to the surface attached Ab (non-fluorescent). and binding will be monitored. If Ag does not bind to the Ab, then it will remain as a freely rotating molecule (black rotating arrow) in the solution. Upon exposure to the polarized light, the fluorescent molecule will be exited and emit the light in a different plane and causes depolarization (blue arrow). Please note, here results are negative as Ag has not bound to Ab. In another case, if Ag binds to Ab; then, the emitted light of the bound antigen remains in the same plane of exited polarized light; because binding to the antibody slows the free rotation of the Ag molecule. Therefore, the light remains polarized (positive result).

Explanations for the wrong answers.

demonstrates a positive response as a depolarization of light

Explanation: From the figure, it can be clear that if Ab will not bind to the Ab (negative result), then only light is polarized.

Does not use Ab as part of the procedure

Explanation: Ab is present in the assay. Its role can be easily seen in the figure.