266

Bioremediation for Sustainable Environmental Cleanup

polymer with the required characteristics and desired functional groups is a costly and time-

consuming method which also generates chemical wastes.

15.4.1.2 Biopolymers

In comparison to synthetic polymers, biopolymers are naturally available biocompatible supports.

Many biopolymers like alginate, chitosan, cellulose, and pectin, etc., are commercially available

and used as supports. Biopolymers possess characters like biocompatibility, availability of various

functional groups, biodegradability to harmless products, non-toxicity and affinity towards proteins.

These characteristics increase the applicability of biopolymers as support for biomolecules and

provide a favourable microenvironment to the attached biomolecule which helps to maintain/

improve biocatalytic aspect of biomolecule.

15.4.1.2a. Alginate: Alginate is a biopolymer which is widely applied for developing supports

of various morphologies and immobilization of biomolecules. Earlier lipase was immobilized in

calcium alginate beads and showed high immobilization yields (Betigeri and Neau 2002), however

reusability was poor due to the leaching of the enzyme from the support. The application of alginate

is limited due to its sensitivity towards divalent ions and low mechanical stability of alginate gels

and substrate diffusional limitations (Coradin et al. 2003). To address the issue, a support comprising

nanosilica-sodium alginate was prepared and chemotherapeutic drug doxorubicin was entrapped

(Mishra et al. 2021a). It was observed that the presence of nanosilica improved the loading efficiency

as well as slowed down the release of entrapped drug.

15.4.1.2b. Chitosan: Chitosan is a mainly used biopolymer as a support because of the presence

of amino groups on its surface. Earlier chitosan microspheres were used for the immobilization

of nuclease (Shi et al. 2011). Glucose isomerase enzyme was also immobilized on chitosan beads

(Cahyaningrum et al. 2014). It was observed earlier that support-comprising chitosan in combination

with alginate showed a lesser leaching effect compared to alginate alone (Betigeri and Neau 2002).

15.4.1.2c. Cellulose and Pectin: Cellulose is an abundantly available natural polymer and it has

been extensively used for the immobilization of various enzymes such as, penicillin G acylase,

α-amylase and tyrosinase (Mislovicova et al. 2004, Namdeo and Bajpai 2009, Labus et al. 2011).

Pectin in combination with chitin and calcium alginate have improved the thermal, denaturant

resistance and biocatalytic properties of entrapped enzymes due to formation of highly stable

polyelectrolyte complexes (Gomez et al. 2006, Satar et al. 2008).

15.4.2 Inorganic Supports

Inorganic supports offer high thermal and mechanical stability, and are resistant towards microbial

attack. These are therefore considered a suitable support for immobilization of biomolecules. In

particular these are important characteristics as inorganic supports have superiority over organic

supports due to their rigidity and porosity. The stiffness of the inorganic supports takes care of the

invariance of pore diameter/pore volume, which further helps to maintain constant volume and

shape to the support itself. It has been observed that inorganic oxides are of more importance and

have wider applicability among other inorganic supports.

15.4.2.1 Inorganic Oxides as Support

Various enzymes (lipase, urease and α‐amylase) have been associated with different inorganic

oxides like aluminium, titanium and zirconium oxides (Yang et al. 2008, Foresti et al. 2010, Reshmi

et al. 2007). It has been reported that inorganic oxides offer high mechanical resistance, stability and

good sorption capacity. These are also inert in different conditions thus could be used as support for

synthesizing biohybrids. Among all, silica-based materials are most preferred support due to their

biocompatibility, high surface area, porous structure, wide availability, ease to functionalization,

high thermal and chemical resistance and good mechanical properties. These characteristics enhance