•
Fluorescein-labeled drug competes with unlabeled drug for antibody
•Sample
excited with plane polarized light (490 nm)
•Fluorescein
emits plane polarized light (520 nm)
•Small,
free drug-fluorescein, rotates faster leading to less emission
•Larger,
antibody-drug-fluorescein, rotates slower and emits plane polarized light (520 nm)
Principle:
Drug in sample competes for antibody with fluorescein bound drug
•More
drug in the sample; less fluorescein labeled drug bound to antibody; lower
emission
of plane polarized light.
•Higher
drug concentration results in lower light emission values.
FPIA
•Available
for a variety of drugs
Advantages
Rapid
turnaround times, sensitivity, ease of operation
Disadvantages
Background
interference in serum sample (requires blank measurement).
All about polarization
