It is performed by shining light on a sample, and measuring the amount of light reflected.
This technique is widely used in clinical
laboratories because it is relatively easily
automated. It is based on the principle that a
dilute suspension of small particles will scatter
light (usually a laser) passed through it rather
than simply absorbing it. The amount of scatter
is determined by collecting the light at an angle
(usually about 70 or 75 degrees).
Antibody and the antigen are mixed in concentrations
such that only small aggregates are formed that do
not quickly settle to the
bottom. The amount of light scatter is measured
and compared to the amount of scatter
from known mixtures. The amount of the
unknown is determined from a standard
curve.
