Nanotechnology-Enabled Sensors

436 Chapter 7: Organic Nanotechnology Enabled Sensors
the near future. As molecular modeling would suggest, the more open barrel
structure, which consists of β-barrels, is more amenable to amino acid
substitutions. For example, the entire transmembranal domain of αhemolysin
can be replaced by a barrel made from a reversed amino acid
sequence. 133 It is unlikely that such a manipulation would work with a helix
bundle in which amino acid side-chain interactions are important for
structural stability of the complex.
7.5 Nano-sensors based on Nucleotides and DNA
The discovery of the fact that deoxyribonucleic acids (DNA), the building
blocks of chromosomes, are the genetic materials in a cell (Fig. 7.55),
was a fundamental leap forward for the biological sciences. The discoveries
around DNA structure and its functionality are recognized as one of the
greatest achievements of our recent scientific history.
DNA structures have numerous applications in the development of sensors
and are believed to have applications as the building blocks of future
nano-devices. This section will present an introduction of these fascinating
structures and will present some of their applications in sensor field.
DNA fragments are used for decoding gene expressions with microarray
sensors. They can be used as selective layers for conductometric sensors. It
changes its properties when exposed to an external source of energy. DNA
has an excellent binary structure with embedded data for the selective detection
of protein structures. DNA fragments are ready-made tools in biology
for the construction of bio-nanomaterials. There are many more to add
to this list.
The ability of cells to store, retrieve and translate the genetic information
is what our lives depend upon. The combination of these activities
maintains a living organism and differentiates it from other materials. At
cell division, this hereditary information is passed on from a cell to its
daughter cell. The information is stored in the genes within a cell, which
are information-containing elements for the synthesis of particular proteins.
As such they determine the characteristics of a species. The number
of genes is approximately 30,000 for humans. The information in genes is
copied and transmitted from cells to daughter cells again and again during
the life of a multicellular organism which is carried out with a supreme accuracy.
This process keeps the genetic code fundamentally unchanged during
the life an organism.
Genetic science emerged in the middle of the twentieth century. In
1940, it was found that in simple fungi the genetic information consists