4. Concluding remark
Many studies have proved that natural clay minerals have good
compatibility with biological enzyme molecules. The enzymes can be
immobilized on clay minerals in the pristine or modified form through
non-covalent adsorption and covalent conjugation. In non-covalent immobilization,
enzymes can be less denatured. The intrinsic structure and
properties of both enzymes and clay minerals are preserved. However,
enzymes immobilized by non-covalent adsorption can desorb from
the clay mineral supports upon the changes in temperature, pH and
ionic strength in liquid media. Such leaching becomes particularly
problematic when such clay mineral enzyme hybrids are used in a
liquid-phase system. In contrast, covalent conjugation provides more
endurable attachment, but the structure of the covalently bound
enzyme may be more easily disrupted. Though the characteristics of layered
clay minerals such as ion exchange, intercalation and surface modification
offer many routes to fine tune the immobilization of enzymes
on them, to preserve the activity of the enzymes with enhancement of
the stability and recyclability are still challenging and need further
investigation.