Preparation of extremely thin solid supported films of lipids by the method of electrostriction

Effects of divalent cations on the formation and structure of solid supported lipid films

The interaction of glassy carbon-supported thin wetting films of lecithin with some divalent cations is investigated by impedimetry and voltammetry. The influence of Ca2+, Mg2+, and Mn2+ on the film structure is explored in two different cases--the divalent cations are added to the electrolyte either before or after the formation of the film. When the film has been previously formed, the addition of divalent cations in millimolar concentrations leads to changes in the passive electrical parameters and the blocking properties of the films. On the one hand the dielectric properties of the film measured in 0.1 M KCl seem to improve after the interaction with divalent cations--the film capacitance decreases, the resistance and resistivity of the film increase. On the other hand the increase of the redox current in the presence of 1 mM Fe(CN)6(3-/4-) in the electrolyte suggests the formation of some defects in the lipid structure of the film after the action of divalent cations. It is shown that the amount of these defects could be significantly decreased when the divalent cations are present in the electrolyte solution before the film formation. The effect of divalent cations on the film stability is tested by applying negative potential to the film. In 0.1 M KCl the films are not stable at potential of - 0.8 V (vs. Ag/AgCl) and are destroyed. The addition of divalent cations stabilizes the films and at certain millimolar concentrations the films remain intact after the action of the negative potential. The effect of Mn2+ is more pronounced, the Ca2+ and Mg2+ have smaller commensurate effect. It is proposed that the changes in the films' properties could be related with more tight packing of the lipid molecules with the divalent cations inserted in the film and that some defects could be opened during the rearrangement of the lipids when the film has been previously formed.

Interaction of thin wetting films of lecithin with some divalent cations

The impact of some divalent cations on the structure of a model membrane system, comprising wetting lipid films, is assayed in this work. The results from impedimetry suggest prominent structural changes upon the addition of the discussed ions to the electrolyte solution contacting the film. These changes are manifested by the increase of resistivity of the films as well as by the decrease of capacitance dispersion. In accordance with other data in the literature, manganese (Mn(2+)) turned out to have an effect greater than those of Mg(2+) and Ca(2+).

Wetting films of lipids in the development of sensitive interfaces. An electrochemical approach

Solid-supported thin liquid films of lipids, contacting an electrolyte phase, turned out to be a dependable system in the field of bosensors. The investigations of these objects during the past decade reveal some of their intriguing features enabling the application in constructions of receptor part with 'two-dimensional' arrangement. As a model system, complementary to the other artificial analogs of biomembranes, the wetting films of lipids offer certain advantages concerning the compromise between the stability and flexibility of the molecular structures involved in sensing. The basic principles underlaying the techniques of formation, as well as the conditions of the films stability are emphasized in the present consized review. While no limitations are imposed by the way of preparation, the films seem especially profitable in conjunction with methods for electrochemical signal transduction. In this regard some prominent examples are discussed.

Electrochemical investigations of cholesterol enriched glassy carbon supported thin lipid films

The formation and study of stable cholesterol enriched thin lipid layers onto the surface of glassy carbon electrode is reported in this work. The method of formation relies on additional thinning of wetting films by electrostriction. Electrochemical techniques based on the concepts of impedance and voltammetry are used to explore the films' features. The impedance data reveal a substantial change of relaxation characteristics of the modified films. In this respect, opportunities for the evaluation of the films' stage based on the approximation with 'constant phase angle element' are discussed. The possible final structure of the films, as well as, their relevance for development of sensor elements are briefly viewed.