Nanotechnology-Enabled Sensors

Fig. 7.36 The general structure of an antibody.
7.4 Proteins in Nanotechnology Enabled Sensors 413
The reactivity of an antigen is restricted to specific parts of the molecules
which are called epitopes. These epitopes specifically bind to the antibody
binding sites, which are also known as paratopes.
The knowledge of the structural formation of antibody-antigen interactions
is mainly based on X-ray diffraction (XRD) investigations. 93 The
area of the antigen epitopes surface comprising between fifteen to twenty
two amino acids interacts with the same number of amino acids on the antibody
paratopes. Many intermolecular hydrogen bonds, ionic bonds, and
salt bridges participate in these interactions and apparently water molecules
also participate in these interactions.
When suspended in water the protein molecules initially repel each
other due to their hydrophilic nature. This force must be overcome before