Biomedical Engineering Reference
In-Depth Information
necessary. Temperatures < 40
°
C are generally enhanced to avoid protein
denaturation.
Products are formed during enzymatic reactions where the substrates
are consumed. h ese compounds can be guided with the suitable trans-
ducers. In the case of glucose oxidase, there are compounds such as O
2
and H
2
O
2
, which are easily detected. Some enzymes have additional active
areas referred to as co-factors, e.g. NADH. h ese co-factors are used for
measuring enzyme activity [1]. For the catalytic activity many enzymes
also requires metal ions.
h e enzyme in biosensors has two important applications. It can either
be used as markers in biosensors ai nity or as catalytic biosensors, such
as immunosensors and DNA sensors. h e concentration of enzyme (E)
is constant and the substrate concentration is much smaller in the cata-
lytic enzyme sensors. When the enzymes are used for labelling antibodies
or DNA strands, the enzyme concentration (E) is the only limiting fac-
tor and the substrate must be used in excess amount. Since the enzymes
have a capability to convert hundreds of substrate molecules per second,
they behave as highly ei cient chemical amplii ers for the detection of
other molecules [2]. Various enzymes are used as labels, such as horse-
radish peroxidise (HRP), glucose oxidase and alkaline phosphatase (AP).
Spectrophotometry and electrochemistry are used for detecting the prod-
ucts of these enzymes. h e products for luminal or luciferin luminescence,
allowing optical detection is delivered through enzyme such as peroxidise
and luciferase.
Enzymes are very sensitive to temperature changes. Increasing in the
temperatures, increase the rate of reaction, but at elevated temperatures,
the protein structure (tertiary structure) denatures, mostly irreversible,
by leaving the enzyme inactive. For most enzymes, the critical tempera-
ture stays between 40
C few enzymes
shows high thermal stability. Enzymes consist of amino acids due to
which it is sensitive to pH. Various species inhibits the enzymes reaction.
Inhibition is reversible, which allows the enzyme to regain full activity
at er dissociation from the inhibitor. h e active sites are being blocked
competitively and alter the enzyme activity by other mechanisms. Other
inhibitors inhibit the enzyme by deactivating it irreversibly. h ese irre-
versible inhibitors work in dif erent way, for example by blocking the
binding site, which react with the central metal ion or the denaturing the
enzyme. Enzyme inhibition sensors have been reported for the detection
of toxic compounds and heavy metal ions and it is commonly based on
the selective inhibition of enzymes [3].
°
C and 50
°
C, however above 100
°
