Radioimmunoassay -
Radioimmunoassay
is
an
extremely
sensitive
method
for
the
detection
and
quantitation
of
any
substance
that
is
antigenic
and
that
can
be
labelled
with
a
radioactive
isotope.
Basically
the
method
depends
upon
the
competition
between
labelled
(known)
and
unlabelled
(unknown)
antigen
for
the
same
antibody.
A
known
amount
of
labelled
antigen
(enzyme
in
this
case),
a
known
amount
of
specific
antibody
and
an
unknown
amount
of
unlabelled
antigen
in
the
sample
are
allowed
to
reach
equilibrium.
By
measuring
the
amount
of
labelled
antigen
bound
to
the
antibody,
a
measure
of
the
antigen
in
unknown
sample
can
be
obtained.
By
suitably
adjusting
the
amounts
of
antibody
and
labelled
antigen,
even
small
amount
of
antigen
in
an
unknown
material
can
be
detected.
