Immobilization methods that are cur

Immobilization methods that are currently being used include absorption, cross-linking, and
self-assembly, whereas materials into which enzymes are incorporated include carbon paste, conducting or non conducting polymers, and different
types of gels. The ultimate aim of these efforts is
to develop an inexpensive and easy-to-prepare
method that can yield a stable matrix possessing
the maximum retention of the biological activity
of the immobilized enzyme. Generally speaking,
physical entrapment of enzymes in polymeric
membranes is one of the most advantageous
methods because it is rapid and simple, the retained enzyme activity is usually quite high, plus
no chemical reaction that may lead to the inactivation of the enzyme is required. The major limi-
tation of physical entrapment is, however, that
unlike chemical immobilization where all types of
substrates, whether they are large or small, can
all reach the immobilized enzyme for interaction,
the physically entrapped enzyme is prohibited
from interaction with large substrates that are
unable to diffuse into the matrix. Therefore, for assaying a large substrate, chemically immobilized enzyme should be used