Antibody-Functionalized Inorganic NPs: Mimicking Nature for Targeted Diagnosis and Therapy - Bioinspired Approaches for Human-Centric Technologies - page 12

Fig. 1.2 Scheme of the possible binding strategies for the attachment of antibodies to the
nanoparticle surface. (a) The physical adsorption, (b) the covalent linkage, and (c) the use of
adapter biomolecules
should be well pondered. Usually, while the choice of the functional group on the
antibody to be used for the binding to the nanoparticle is more restricted, due to the
risk to compromise the binding efficiency of the antibody toward the antigen, the
introduction of the proper functional group on the nanoparticle is easier and allows
more freedom in the design of the functionalized nanoparticles carrying the proper
binding moieties. Among the different coupling chemistries, the amino-carboxyl
chemistry is considered the most used and straightforward in aqueous media.
In some works, the primary amino groups of the antibody, either the amino end
groups or the ɛ -amino lysine present all over the antibody proteins, have been used
for the coupling reaction. However, the amino-terminated groups are present in the
proximity of the antigen binding sites of the antibody, and therefore they are not the
most suitable choice. This is because, upon linkage to the nanoparticles, their bulky
size might hinder the antigen binding site, with consequent loss of the antigen
binding capacity. On the contrary, if amino-functionalized nanoparticles are used,
the presence of the carboxyl-terminated functionalities on the Fc region of the
antibody (see Fig. 1.1 ) can be exploited. The Fc region in the 3D configuration of
the antibody is quite distant from the antigen binding site, and it is not involved in
the binding with the antigen. To amino-bearing nanoparticles, together with the
carboxyl-terminated functional group of the antibody, also carboxyl-bearing amino
acid (i.e., glutamic and aspartic acid) residues of the antibody may react. However,
given the bulky structure of the three-dimensional configuration of the protein, the
carboxyl-terminated groups are more exposed than the carboxyl-bearing amino