Nanotechnology-Enabled Sensors

384 Chapter 7: Organic Nanotechnology Enabled Sensors
intend to sense relatively large targets (in comparison with single molecules)
such as nano-particles.
Fig. 7.14 SAMs with a mixture of two different self-assembled molecules. One is
utilized for sensing and the other is employed to space those sensing molecules.
7.2.7 Layer-by-Layer Assembly
The layer-by-layer (LbL) assembly method can be regarded as a versatile
bottom-up nanofabrication technique. The LbL deposition technique
offers an easy and inexpensive process for the formation of multilayered
materials and allows a variety of materials to be incorporated within the
film structures. 15
Over the past decade, by using the self-assembling nature of artificiallydesigned
molecules, many types of nanoscale molecular assemblies have
been developed. 16 This includes molecular recognition-directed molecular
assemblies, 17,18 surfactant bilayer membranes, 19 Langmuir–Blodgett
films, 19 self-assembled monolayers, 20 and alternately deposited polyelectrolyte
multilayers. 21 LbL assembly is an approach based on the alternating
adsorption of different materials containing complementary charged or
functional groups to form ultratin layers. This method generally uses oppositely
charged species and the level of control over the film composition
and structure is down to several nanometers. 22
The classical LbL approach developed by Decher is an interesting example.
21 They used the electrostatic attraction between oppositely charged
molecules as a driving force for the multilayer buildup. The process is depicted
in Fig. 7.15 for the case of polyanion-polycation deposition on a
positively charged surface. Strong electrostatic attraction occurs between a
charged surface and an oppositely charged molecule in solution. In princi-