Nanotechnology-Enabled Sensors

402 Chapter 7: Organic Nanotechnology Enabled Sensors
streptavidin then they can bind to biotinylated molecules. 83 A review of
SPR sensing methods for controlled coupling to carboxymethyldextran
surfaces can be found in the paper by Löfas et al. 84
Fig. 7.28 A schematic diagram of the two-channel integrated miniature SPR sensor
with a detachable flow cell. On the left, the frontal view shows the two channels
which are laser-cut in the silicone rubber gasket. On the right is the side view
of the sensor with the flow cell attached, showing the functional components of
the sensor. Reprinted with permission from the Elsevier publications. 85
The incorporation of nanoparticles of predetermined dimensions which
are bound to organic molecules in immunoassays can be used for increasing
the sensitivity of conventional chromatic assays. Commercial mass
sensors based on quartz crystal microbalance (QCM) or surface acoustic
wave (SAW) devices, which are used for the sensing affinity between different
organic molecules, are becoming more available.
QCM electrodes are generally made of gold. Such a gold surface is excellent
for the formation of SAMs, electrostatic bonds, etc. For instance,
Carusu et al 86 used QCMs with gold electrodes for DNA sensing. They
employed both covalent bonds, which were established using carbodiimide
hydrochloride and N-hydroxysuccinimide (NHS), and electrostatic bonds
using poly(allylamine hydrochloride) (PAH). Immobilisation by silanising
the surface, for instance with γ-aminopropyltriethoxysilane activated with
glutaraldehyde, is also frequently employed on QCMs. 87,88
Electrochemical sensors can also take advantage of surface Fictionalization.
Recently, the electrochemical properties of nanomaterials such as