Radioimmunoassay (RIA)

Important points to remember (And to impress the examiner :p )

1. First developed in 1960 by two endocrinologists, S. A. Berson and Rosalyn Yalow, to determine levels of insulin–anti-insulin complexes in diabetics.
2. Sensitive technique - measures hormones, serum proteins, drugs, and vitamins at concentrations of 0.001 micrograms per milliliter or less.
3. Antigen is generally labeled with a gamma-emitting isotope such as 125 I, but beta-emitting isotopes such as tritium (3 H) are also routinely used as labels.

Principle: 

RIA involves competitive labeling of the labeled and the unlabeled antigen to the antibody.

Labeled antigen at a saturation concentration (don't worry,it means concentration at which all the binding sites of antibodies are occupied)  + Antibody

Then test samples of unlabeled antigen of unknown

concentration are added in  larger 

amounts.

Now here, the antibody is unable to recognize the difference between the labeled and the unlabeled antigen,so 

the two kinds of antigen compete for available binding sites on the antibody.

As the concentration of the unlabeled antigen increases, the antibody just like a betraying friend or any douchebag boyfriend unbinds the already labeled antibody, and like a snatchy girlfriend the unlabeled antigen displaces the labeled one and occupies the site.

The decrease in the amount of radiolabeled antigen bound to specific antibody in the presence of the test sample is measured in order to determine the amount of antigen present in the test sample.

To determine the amount of labeled antigen bound, the Ag-Ab complex is precipitated to separate it

from free antigen (antigen not bound to Ab), and the radioactivity in the precipitate is measured. 

A standard curve can be generated using unlabeled antigen samples of known concentration (as a standard sample), and from this plot the amount of antigen in the test mixture may be precisely determined.

Thanks you.

Lots of Love <3

-Staph.