Affinity binding can also lead to a reversible immobilization
method. The use of streptavidin–biotin affinity is commonly
employed for protein immobilization on magnetic nanoparticles
in immunoassays. Some works also use affinity ligands such as
inhibitors, for purifying a complex mixture of enzymes.
Another affinity binding method uses gold shell-coated magnetic
nanoparticles. The affinity is either due to the cysteine
residues from proteins, or due to the attachment to a suitable
molecule on the particle surface