Nanotechnology-Enabled Sensors

374 Chapter 7: Organic Nanotechnology Enabled Sensors
Covalent bonds are strong. The interactions are relatively fast (comparing
with other bonds) and very well controlled. However, the processes of
their formation are generally complex and require synthetic steps which
can be both costly and time consuming.
Cross-linking has similar advantages and disadvantages to covalent
bonding. However, it provides flexibility in establishing an interaction by
providing relevant functional groups. It is strong but it also has the disadvantage
of being able to degrade the material’s biocompatibility.
Quite often, the direct coupling of one functional group to another is not
energetically favorable; hence functional groups may need to be reacted
with an intermediate compound, in order to be made more reactive. This
process is called activation. For many molecules that are soluble in organic
solvents, a wide range of activators and coupling reactions can be employed.
Unfortunately, many of these reactions that are widely used in
organic synthesis chemistry cannot be utilized for biomolecules such as
proteins. This is due to the fact that the coupling processes of such biomolecules
need to be carried out in mild conditions in order to avoid deteriorating
functionality of the biomolecules which limits our options.
There are a plethora of different types of bonds for covalently coupling
functional groups. Some of the most widely utilized covalent coupling
strategies will be outlined in this section.
Application of carboxylic acids
Carboxylic acids are organic molecules that contain a carboxyl group,
which is a carbonyl group –(C=O)– whose carbon atom is bonded to a
hydroxy (–OH) group. It has the formula –C(=O)–OH, usually written as
–COOH. 4 In determining the name of a carboxylic acid, the total number
of carbon atoms in the longest chain is counted, including the one in the
–COOH group. Some examples of such compounds are shown in Fig. 7.3.
H
O
OH
C
H 3
O
OH
C
H 3
CH 2
methanoic acid ethanoic acid propanoic acid
Fig. 7.3 Some carboxylic acids.
O
OH