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3 Immobilized Enzymes for Bioconversion of Waste to Wealth

simple magnet. The immobilization of an enzyme on nanoparticle can able to place

excess of biological activities on a very small surface area, and it can also create

hybrid assemblies. When nanomaterials are used as solid supports, all the benefits

of the immobilized enzymes on nano-sized particles are inherited. The methods

of immobilization, for example, adsorption, covalent bonding, encapsulation, or

entrapment which are used with the solid supports of conventional sizes can also

be used for the immobilization on the nanomaterials.

Iron oxide (Fe3O4) nanoparticles are extensively used as superparamag-

netic supports. The immobilization of enzymes on Fe3O4 was done by several

approaches. Commonly, iron particles are coated with other materials which can be

functionalized with different groups and these can be used for coupling to enzymes.

Covalent coupling can result into certain loss of enzyme activity. In the case where

the coating material is porous, various enzyme molecules can be immobilized

inside the porous coating.

Adsorption of enzymes by non-covalent interaction and with or without coating

will be gentler, and the enzymes will generally retain higher biological activity.

In the event of bioaffinity method, the fusion tags will be made to have specific

affinity to either iron oxide or silica coat on the nanoparticles. Both the single-

and multi-walled nanotubes (MWNTs) have been generally used for the enzyme

immobilization process. Poly-nanofibers have been also used as carriers for the

enzymes, and these fibers can be produced by electrospinning. Additionally,

nanotechnology will offer various alternatives for the enzyme encapsulation like

nanosheets, nanovesicles, etc. Silica particles are of great interest for the enzyme

immobilization since they provide an opportunity to introduce chemical functional

group on their surfaces which in turn provide biological molecular interaction [30].

Nanoparticulate materials provide wide advantages as the supporting materials

for the enzyme immobilization which include higher surface area allowing more

enzyme loading, lower mass transfer resistance, and improved stability.

Maltogenic amylase and α-amylase were co-immobilized by a method based on

nano-magnetic combi cross-linked enzyme aggregates [31]. These co-immobilized

enzymes were used for the production of maltose from corn starch and they retained

original activity for 10 cycles with improved thermostability [31]. Nanocomposite

beads of chitosan–montmorillonite were used for the immobilization of α-amylase,

and immobilized enzyme showed high pH and thermal stability in addition to

retaining its 64% of original activity after 40 days [32]. Reusability and retention

of α-amylase activity were improved by immobilizing the enzyme in nanoporous

composites of polyacrylamide–graphene [33]. Similarly, β-amylase was immobi-

lized onto graphene oxide nanosheets, carbon nanotube composite, and iron oxide

nanoparticles to improve the retention of activity at higher temperature.

Pectinase enzyme was immobilized on magnetic nanoparticles grafted with

trichlorotriazine-functionalized polyethylene glycol [34]. This immobilized enzyme

functions as robust nanobiocatalyst for the clarification of fruit juice [34]. Pectinase

and cellulase were co-immobilized onto magnetic nanoparticles in order to extract

antioxidant from waste fruit peels [35]. Immobilization of chitosan–cellulase

nanohybrid onto alginate beads was done, and these beads were successfully used