Chemistry Reference
In-Depth Information
4.4
Bioinspired Silica for Enzyme Immobilisation
Biology produces nanostructured silica under environmentally-friendly green con-
ditions. Extensive research has been undertaken in order to successfully find ways
to transfer the bio-based methods into synthetic approaches to establish bioinspired
silica technology. These methods, for inorganic materials synthesis, are green, rap-
id, controlled, mild and do not require non-aqueous solvents. Furthermore, such
bioinspired synthesis allows material properties to be explicitly tailored.
Mild synthetic conditions of bioinspired silica formation have allowed the for-
mation of nanostructured silicas containing peptides, proteins and enzymes [
69
].
A key advantage of using bioinspired method is that the materials properties (e.g.
surface area, particle size, porosity, etc.) can be fine-tuned through the use of appro-
priate processing parameters, additives and silica precursors. This rapid, one-step,
in situ
method, when applied to enzyme immobilisation route, has great potential
over existing routes due to its short preparation time, mild conditions and, as sub-
sequently detailed, its flexibility [
2
,
69
]. An extensive list of enzymes immobilised
using bioinspired silica supports is tabulated in Table
4.5
.
Initial studies concentrated on using the R5 peptide, which is a synthetic silica
precipitating peptide, based on a naturally occurring silaffin protein found in the
silica skeleton of the
Cylindrotheca fusiformis
diatom, as an additive. A range of
enzymes including catalase, horseradish peroxidase and β-Galactosidase have been
successfully immobilised using the R5 peptide, with all reporting very high lev-
els of activity being maintained and good enzyme stability (Table
4.5
) [
45
,
76
].
Although, R5 peptide proved successful in immobilising a range of enzymes, the
peptide is, however, expensive to obtain [
2
,
74
].
From Table
4.5
it can be seen that several different additives, most of which are
cheaper than R5 and readily available, have been used to produce silica capable of
immobilizing a host of enzymes, all with varying success. Polyethyleneimine (PEI)
has had varying success. Poor results were observed for lipase and carboxylesterase
immobilisation, with significant loss of activity being observed compared to free
enzyme [
77
,
78
]. It did, however, appear efficient for horseradish peroxidase im-
mobilisation [
79
]. Polyallylamine (PAH) has also had reasonable results. It has been
used to successfully immobilise lipase and D-amino acid oxidase, with 51 and 96 %
of the enzyme's activity being maintained respectively [
80
,
81
]. Polyamidoamine
dendrimers (PAMAM) and poly-L-lysine (PLL) have also proved successful in im-
mobilising several enzymes. PAMAM has been used to immobilise glucose oxidase
and horseradish peroxidase (with limited success) [
79
,
82
], while PLL has been
used to immobilise several enzymes including adenosine deaminase [
83
].
As is evident from Table
4.5
, as well as for chemical processes, the immobilised
enzymes produced using these methods have the potential to be used in other ap-
plication, such as for use in biosensors, microfluidic devices and as anti-fouling
coatings; many applications also involve integrating the immobilised enzymes onto
surfaces [
2
,
45
,
84
]. This range of applications is likely to contribute to an increase
in interest towards these bioinspired routes.
