A new class of molecular system is designed by the use of Langmuir-Blodgett (LB) and Self-Assembly (SA) techniques. Its specific properties are:
i) multilayer structure consisted from the layers of a nucleic acid alternated with the layers of cationic amphiphiles or polycations;
ii) insolubility of the films in water-salt media both with their good hydrophility and permeability for different ligands. The film may be formed onto any type of solid support and its chemosensitivity can be analyzed by a number of electric, magnetic, optic and other physical methods;
iii) immobilization of a nucleic acid in the film is achieved by electrostatic interaction with polycation or cationic amphiphilic molecules. This is an important difference from other nucleic sensors in which the covalent bonds are used for polynucleotide immobilization. Only the special types of supports are suitable to form the covalent bonds which disturb the secondary structure of nucleic acid in the neighboring area of the linkages;
iv) the possibility to fabricate the films with any signs of electric charge on the cover layer;
v) finally, the most important property of the films is the high level of nucleic acid ordering in them. The change of the ordering resulted from the binding of a ligand leads to multiple increase of sensitivity of corresponded film.
Spectrophotometric investigation of the films was aimed to find out the ways to vary their sensitivity and selectivity in respect to such ligands as nucleic monomers and intercalators of DNA double helix. Both types of ligands bound first of all with nucleic component of the film. Intercalators - via electrostatic and Van-der-Vaals interactions and nucleic monomers - by formation of hydrogen bonds with the bases of nucleic acid from the film.
The binding of nucleic monomers by [poly(C)-PAM] SA-film from multicomponent mixtures of adenylic, cytidylic, thymidylic and guanylic nucleosides or nucleotides demonstrated high selectivity in respect to guaninylic monomers which are complementary to cytosine bases of poly(C). A high difference in the binding was also found between nucleosides and 5'-mononucleotides and between 2'-3' and 3'-5' cyclic nucleotides.
LB- and SA-films contained double helical DNA were examined on the binding of antitumour drug daunomycin. Two methods of drug detection were used: the measurement of light absorption by the drug which bound with the film and CD measurement of DNA packing and/or its conformation in the film which is immersed in daunomycin solution. CD method which test the film structure was found up to 100 times more sensitive than UV-VIS absorption of the ligand bound (10-7 and 10-5 M of the drug respectively).