Development of polyelectrolyte multilayer films and their applications to analytical chemistry (Review)

The development of polyelectrolyte multilayer films (PEM) is reviewed in re lation to their applications to analytical chemistry. PEMs are constructed by a layer-by-layer deposition of oppositely charged polyelectrolytes on a solid surface from aqueous solutions. The PEM films are formed through an e lectrostatic force of attraction between polycation and polyanion. The stru cture of PEM films depends significantly on the properties of the bathing s olution, including the concentration of polyelectrolytes, ionic strength, a nd pH. High ionic strength solutions usually result in thicker film. It is known that hydrogen bonding and hydrophobic interactions also play a role a s a secondary force in addition to the electrostatic interactions. Function al PEMs have been prepared using charged dyes, metal and inorganic particle s, DNA, proteins, and virus. Analytical applications of PEM include coating the inner wall of capillaries for electrophoretic separation, pervaporatio n films for alcohol/water purification, sensitive layers of gas and humidit y sensors, surface modification of functional electrodes, and ion-sensitive PEMs for optical ion sensors. Protein-containing PEMs are finding wide app lications to immuno, sensors, enzyme sensors, bioreactors, and bio-fuel cel ls, in which proteins are still active in the PEM films.