What are the three major types of immobilizing enzymes and give a brief description of each

There are three different ways by which one can immobilize an enzyme, which are the following, listed in order of effectiveness:

Adsorption on glass, alginate beads or matrix: Enzyme is attached to the outside of an inert material. In general, this method is the slowest among those listed here. As adsorption is not a chemical reaction, the active site of the immobilized enzyme may be blocked by the matrix or bead, greatly reducing the activity of the enzyme.
Entrapment: The enzyme is trapped in insoluble beads or micro spheres, such as calcium alginate beads. However, this insoluble substances hinders the arrival of the substrate, and the exit of products.
Cross-linkage: The enzyme is covalently bonded to a matrix through a chemical reaction. This method is by far the most effective method among those listed here. As the chemical reaction ensures that the binding site does not cover the enzyme's active site, the activity of the enzyme is only affected by immobility. However, the inflexibility of the covalent bonds precludes the self-healing properties exhibited by chemoadsorbed self-assembled monolayers. Use of a spacer molecule like poly(ethylene glycol) helps reduce the steric hindrance by the substrate in this case.

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