What are the methods of immobilising enzymes?

There are four methods of enzyme immobilisation: adsorption, covalent bonding, entrapment and membrane separation.

Adsorption involves mixing the enyzme with an immobilsing support so the enzyme molecules will bind to it because of hydrophobic interactions and ionic links. The support is called an adsorbing agent and could be porous carbon, glass beads or clays.

Covalent bonds between enzyme molecules and an insoluble material, such as clay, are formed using cross-linking agents (e.g. sepharose).

Entrapping the enzyme molecules in a network or gel beads or cellulose fibres allows the enzyme to be immobilised in their natural state (not attached to another molecule). 

Membrane separation physicially separates the enzyme and substrate solutions with a partially permeable membrane. Both the substrate and product molecules are small enough to pass through the membrane.