POLYELECTROLYTE SELF-ASSEMBLING
(LAYER-BY-LAYER TECHNIQUE)

The method is based on the successive deposition of oppositely charged polymers onto solid surfaces [1, 2]. The following scheme can illustrate the method.

Hydrophilic and positively charged substrate is immersed into the solution of polyanion (negatively charged polymer, for example, PSS) for several minutes. As a result, a thin layer of the polymer is adsorbed on the surface. The thickness of the formed layer is of about 1 nm. Overcompensation of charges leads to negative surface charge density. The further growth of the thickness does not take place due to the electrostatic repulsion. Then, the substrate is washed (a washing step is needed to remove supernatant material) and placed into the solution with polycation (positively charged polymer, for example, PAH). The polymer is attached electrostatically to the charged surface forming a layer of about 1 nm thickness. Again, the further growth of the thickness is blocked as it is now charged positively and electrostatic repulsion with polymer molecules in the solution takes place.

The procedure can be repeated for the desirable number of times providing the layer of necessary thickness with nanometre resolution.

The main advantages of the method are: simplicity, absence of expensive equipment, and possibility of covering practically any surface.

Another and very important advantage of the technique is the possibility of the integration of other objects into the structure, such as proteins [3], DNA [4], nanoparticles [5], and even viruses [6].

1. GDecher, J.D Hong, J. Schmitt
   Thin Solid Films 210: 831-835 (1992)

2. YLvov, G. Decher, H. Mohwald 
   Langmuir 9: 481-486 (1993)

3. E. Brynda, J. Pachernik, M. Houska, et al.
    Langmuir 21: 7877-7883 (2005)

4. K.F. Ren, J. Ji, J.C. Shen
    Macromolecular Rapid Communications 26: 1633-1638 (2005)

5. J.W. Ostrander, A.A. Mamedov, N.A. Kotov  
   Journal Of The American Chemical Society 123: 1101-1110 (2001)

6. Y. Lvov, H. Haas, G. Decher, et al. 
   Langmuir 10: 4232-4236 (1994)