Design of enzyme electrode and their application?


An enzyme electrode is the union of an enzyme, that biologic catalyst which acts sensitively and specifically with almost all organic and inorganic compounds in nature, with an
electronic sensor (an ion-selective electrode). The result is
an electrode that is useful for the assay of organic and inorganic compounds, in a manner as simple as a pH measurement with a glass electrode.

The principle of the enzyme electrode is simple: an enzyme is used which reacts with the compound to be assayed
either specifically or selectively. This enzyme, in an immobilized or insolubilized form, is placed onto a conventional ionselective electrode which measures either the decrease of one
of the reactants (i.e., O2 in the oxidation of uric acid or glucose) or a product (i.e., CO2 from an amino acid). The substance to be assayed diffuses into the layer of the enzyme in
the electrode, producing or consuming an electroactive substance; this is sensed by the base electrode. The potential or
current produced is a function of the concentration of the
substance assayed.

commercially available (or homemade) electrodes
have been used and can be used in construction of enzyme
electrodes: (1) glass electrodes-H+
and monovalent cation;
(2) gas-NH3, CO2)
and O2; (3) solid and "solid" liquid
membrane electrodes-NH4
, S~, CN~, and I"; and (4) Pt

Two basic techniques may be used in assay with enzyme
electrodes, kinetic and equilibrium. In the kinetic method,
the rate of change in the potential or current at the electrode
is measured, with the first 10-30 sec of response. This
change, AE or Ai/At, is then related to the content of substance to be assayed. In the equilibrium method, the steadystate current or potential, i or E, is measured and related to
the concentration. This relationship is logarithmic in the
case of potential (E) and linear in the case of current (i). The
rate method is faster and eliminates the possibility of error
due to side reactions that may consume the electroactive

Ans By-
Gr. Noida