Biomedical Engineering Reference
In-Depth Information
Recently, the layer-by-layer (LBL) adsorption technique based on electrostatic force
between polyelectrolytes and proteins has received great attention and interest. A novel tech-
nique proposed by Decher and Kunitake, LBL, has been introduced to fabricate multilayer
films, and it represents a promising preparation method because no complicated instruments
or chemical reactions are involved and ultrathin multicomponent architecture can be con-
structed simply by alternate adsorption in cationic and anionic polyelectrolytes [3,4].
8.2
Preparation of Layer-by-Layer Film on a Solid-State Device
LBL method is based on the electrostatic force between polyanions and polycations.
Generally, in the LBL adsorption process, the substrate (after proper pretreatment) is
immersed in a beaker containing either a polycationic or polyanionic solution for a given
period of time (usually a few minutes), and then washed in a solution of approximately
the same pH to remove nonadsorbed molecules. The substrate is then immersed in
another solution containing the oppositely charged polymer and washed again. By repeat-
ing the alternate adsorption steps in oppositely charged polyelectrolyte solutions, a mul-
tilayer structure can be formed. A schematic illustration of the formation of multilayer
structures composed of polyelectrolytes or other charged molecular or colloidal objects is
shown in Figure 8.1.
In fact, the LBL method is dependent on charge neutralization and resaturation between
polycations and polyanions, and the procedure of LBL can be regarded as a template con-
trolled growth process. First, the solid surface acts as a template, and after the adsorption,
it is refunctionalized and acts as a new template for the following adsorption. The multi-
layer film grows according to the above steps, and the effective electrostatic force between
the oppositely charged layers is critical. For this reason, an ideal adsorption is not only the
adsorption of one layer but also the overcompensation of the electric charges of previous
layers and the supply of additional charges to facilitate further adsorption.
Unlike the chemisorption method, multilayer film could be fabricated on various kinds
of inorganic substrates such as glass [5], quartz [6], silicon wafers [7], metals [8], and others
1. Polycation
2. Rinsed
3. Polyanion
4. Rinsed
FIGURE 8.1
(See color insert following page 330)
Multilayer assembly of oppositely
charged polyelectrolytes by layer-by-
layer (LBL) method.
4
1
2
3
