MONOMOLECULAR LANGMUIR-BLODGETT-FILMS AT ELECTRODES - FORMATION OF PASSIVATING MONOLAYERS AND INCORPORATION OF ELECTROACTIVE REAGENTS

Langmuir-Blodgett (L-B) transfer of mixed octadecanethiol (C18SH)-octadecanol (C18OH) monlayers onto vapor-deposited gold films on glass slides leads to the formation of stable, densely packed monomolecular films when the composition of the mixed monolayers involves 60-80 mol % octadecanethiol. This composition of the mixed L-B films is a result of a trade-off between the mole fraction of C18OH, whose increasing magnitude allows one to increase surface pressure of a mixed monolayer during an L-B transfer, and the mole fraction of C18SH, whose increasing magnitude enhances stability of the mixed monolayer on the gold surface following the L-B transfer. The passivating properties of C18SH/C18OH L-B monolayers were investigated electrochemically. Determination of interfacial capacitance and measurements of the extent of permeability of the surface monolayers by cyclic voltammetry demonstrated that the passivating characteristics of the C18SH/C18OH L-B monolayers are essentially identical to the best self-assembled octadecanethiol monolayers described in the literature. L-B transfer of monolayers containing small quantities of an electroactive reagent can be used as a general technique of reagent immobilization at the electrode surface. Unlike self-assembly methods, reagent incorporation in Langmuir-Blodgett monolayers offers precise control of their composition in a broad range of concentrations. Comparison of the surface concentrations of ubiquinone incorporated in C18SH/C18OH monolayers at the air/water interface before L-B transfer and at the electrode surface following L-B transfer gave 1:1 correlations in the concentration range 1.0 x 10(-12)-1.0 x 10(-10) mol/cm2.