Which statement about fluorescence polarization is true?

Which statement about fluorescence polarization is true?

• A. Plane-polarized light is used for sample excitation.
• B. Small molecular complexes show a greater amount of polarization.
• C. It is a heterogeneous technique employed in fluorophore-ligand immunoassays.
• D. Polarized light detected is directly proportional to concentration of ligand in sample.

Answer: (A)

In fluorescence polarization, what you’re measuring is how fast the fluorophore rotates during its excited state. If the excitation light is plane-polarized, the emitted light’s polarization reflects how much the molecule has rotated before emitting a photon. Because rotation slows for bigger molecules or for fluorophores that are bound in complexes, the emitted light stays more polarized when the molecule is larger or bound. This makes the statement about using plane-polarized light for excitation true. On the other hand, smaller molecules rotate quickly and depolarize the emitted light more, so they show less polarization. That’s why the idea that small molecular complexes have greater polarization isn’t correct—the opposite is true. Fluorescence polarization is typically a homogeneous assay, where binding changes the rotational mobility without separating bound from free species; describing it as heterogeneous isn’t accurate. Finally, the polarized signal isn’t simply directly proportional to ligand concentration. It reflects the fraction bound and the resulting rotational mobility, which depends on binding affinity and assay design, not a straight line with concentration.

In fluorescence polarization, what you’re measuring is how fast the fluorophore rotates during its excited state. If the excitation light is plane-polarized, the emitted light’s polarization reflects how much the molecule has rotated before emitting a photon. Because rotation slows for bigger molecules or for fluorophores that are bound in complexes, the emitted light stays more polarized when the molecule is larger or bound.

This makes the statement about using plane-polarized light for excitation true.

On the other hand, smaller molecules rotate quickly and depolarize the emitted light more, so they show less polarization. That’s why the idea that small molecular complexes have greater polarization isn’t correct—the opposite is true.

Fluorescence polarization is typically a homogeneous assay, where binding changes the rotational mobility without separating bound from free species; describing it as heterogeneous isn’t accurate.

Finally, the polarized signal isn’t simply directly proportional to ligand concentration. It reflects the fraction bound and the resulting rotational mobility, which depends on binding affinity and assay design, not a straight line with concentration.