Chemistry Reference
In-Depth Information
Fig. 4.5
Typical sol-gel process adopted for enzyme immobilisation. Image reproduced with
permission [
68
].
DGS
= diglycerylsilane;
SS
= sodium silicate;
Evap.
= alcohol removal by
evaporation
typically silica [
2
,
10
,
41
,
66
]. Alternative approaches of entrapment and encap-
sulation include hydrogels such as polyacrylamide gels [
7
,
67
], immobilising the
enzyme by using fibres, using semi-permeable membrane microcapsules or usinf
polyelectrolyte micro-capsules [
40
].
The sol-gel route is, however, very common and this is largely due to its versa-
tility, since it is compatible with a vast range of enzymes, including lipase, cata-
lase and peroxidase [
68
]. We have recently reviewed elsewhere this method for
the formation bio-hybrids [
69
] and a brief summary is provided in the following. It
involves the hydrolysis and subsequent condensation and aggregation of alkoxysi-
lanes, resulting in the creation of a gel or particulate-like silica network [
2
,
70
]. The
enzyme is added during this, resulting in its entrapment within the gel (Fig.
4.5
). For
entrapment/immobilisation methods in general, a major advantage is that modifica-
tions to the enzymes are minimal since the support simply confines the enzyme to
restrict its movement, and as a result, high activities can be maintained. Since no
direct attachment of the enzyme to the support occurs, active sites do not become
blocked by the support, as is a problem for the attachment methods. Enzyme stabil-
ity is also typically increased due to the surrounding shielding structure; this there-
fore increases applications at more extreme conditions.
