Nanotechnology-Enabled Sensors

7.4.4 Using Proteins as Nanodevices
7.4 Proteins in Nanotechnology Enabled Sensors 411
In this section we will present a selection of protein-based components
for the development of nanodevices as well as nanomaterials which can be
useful in sensor technology.
The conformations of proteins give them their unique functions based
on their chemical properties. Proteins units can be engineered for conducting
specific chemical reactions. The chemical and physical properties of a
protein give it the ability to perform extraordinary dynamic processes.
The biological properties of a protein depend on how it interacts physically
and chemically with other molecules. For instance, antibodies attach
to certain viruses or bacteria, enzymes can interact with substrates and
molecules such as ATP (which will be explained later in this chapter) to
catalyze reactions in proteins. Actin molecules attach to each other to form
an actin filament which are extremely abundant in eukaryotic cells where it
forms one of the major filaments of the cytoskeleton which gives shape to
a cell. 92
The binding of proteins to other chemicals is not always strong; in many
cases it is actually weak. However, the binding always shows specificity,
which means that each protein can only bind to one or at most a few molecules
that it encounters. Such a nature can be efficiently used for making
sentitive surfaces. The substance which is bound by a protein is called a
ligand for that protein. This ligand can be an ion, a small molecule or a
macromolecule. Ligand-protein binding is of great importance in sensor
technology.
Noncovalent bonds such as hydrogen bonds, ionic bonds, and the Van
der Waals attractions as well as hydrophobic interactions are responsible
for the ability of selective bind of a protein to a ligand. The effect of each
bond can be weak but the simultaneous formation of many weak bonds between
the protein and the ligand form the selective binding. Even the
matching of the surface contour of the protein and ligand can be the reason
for selective binding (Fig. 7.35), as molecules of the wrong shape cannot
approach the active sites closely enough to bind, if indeed they could. The
region of a protein that associates with a ligand is called a binding site.
These sites usually consist of a cavity in the protein surface which is
formed by the folding arrangement of the polypeptide chains.