Immobilisation of enzymes involves trapping enzyme molecules within calcium alginate beads formed by dripping an enzyme-sodium alginate mixture into a calcium chloride solution. This prevents the enzyme from contaminating products and allows it to be recovered and reused through a column system. Immobilisation can also enhance enzyme stability and allow catalysis under unfavorable conditions. Glucose dipsticks and biosensors use the enzyme glucose oxidase to catalyze a reaction that produces a detectable product, such as hydrogen peroxide or a change in oxygen concentration, signaling the presence of glucose.

1. Immobilisation of enzymes
• Immobilisation of an enzyme in alginate beads
(e.g. amylase):
– Amylase enzyme is mixed with a solution of sodium
alginate
– This mixture is dripped (usually through syringe) into
a solution of calcium chloride
– The sodium ions are displaced by the calcium ions –
formation of hard, insoluble beads of calcium
alginate, in which are trapped the molecules of
amylase
– The alginate beads are left to harden further – they
are rinsed
– Beads are normally placed in a suitable container to
create a column of beads
– Suspension of starch can then be trickled down the
column and collected in a beaker
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3. • Advantages of immobilisation:
– Enzyme can be recovered after use using a
very coarse filter rather than a molecular filter
– Enzyme does not contaminate product
– Immobilisation may enhance stability
(thermostability or pH-stability) of the enzyme
molecule as it is supported
– Substrate can be easily passed through the
enzyme several times
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4. Advantages of immobilisation Disadvantages of immobilisation
1. Easier to separate enzyme and 1. Immobilisation may alter shape of
products enzyme
2. Allows catalysis in unfavourable
2. May alter catalytic ability
media
3. Increases stability and can be
3. Enzyme may become detached
manipulated easily
4. Allows continuous
4. Expensive
production/enzyme used for longer
5. Enzyme can be recovered and
reused
6. Enzyme does not contaminate
product/no purification required
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5. The use of dipsticks and biosensors in the
quantitative measurement of glucose
• One way to determine the quantity of insulin
needed by diabetics is to test a sample of urine
with a glucose dipstick
• The dipstick has the enzyme glucose oxidase -
oxidises glucose into hydrogen peroxide and
gluconic acid
• Hydrogen peroxide will oxidise indicator chemical
on dipstick – colour change
• Colour change related to concentration of
glucose in urine sample – colour chart
• http://www.irvingcrowley.com/cls/urin.htm
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6. • Biosensor: a device which uses a biological
material, such as an enzyme, a cell or an
antibody to detect or measure a chemical
compound
• Reaction between the biological material
and the chemical being measured brings
about a change which is converted to an
electrical signal by an appropriate
transducer
• Electrical signal is then amplified to give a
read-out on a digital display
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7. • The glucose biosensor works as follows:
– It contains a layer of immobilised glucose oxidase
enzyme
– Enzyme binds with any glucose in the blood, which is
oxidised with dissolved oxygen from the solution to
form hydrogen peroxide and gluconic acid
– An electrode (usually platinum) measures the drop in
oxygen concentration as it is used to make hydrogen
peroxide – electrode generates an electrical signal
– The size of the electrical signal is proportional to the
concentration of glucose in the blood
– A digital readout gives the user a figure for the
glucose concentration
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