Scanning electrochemical microscopy of liquid/liquid and liquid/membrane interfaces

The kinetic and the mechanistic aspects of charge transfers (ET and IT) across the liquid/liquid interfaces were investigated using scanning electrochemical microscopy (SECM). The rate constant of ET across the two immiscible electrolyte solutions (ITIES) is essentially independent of interfacial potential drop in the absence of interfacial adsorption of the common ion when the organic redox reactant is a neutral species. This result is in agreement with the widely accepted three-layer model of the ITIES. However, when a spacer (e.g., a molecular monolayer of a long-chain lipid) prevents the reactants from coming very close to the phase boundary, the interfacial potential drop between the aqueous and organic redox species increases, and the true potential dependence of the rate constant can be observed.; The solvent dynamics effect on ET at the ITIES was observed for the first time. The rate of the ET from ZnPor to Ru(CN)₆3− at the DCE/water interface was about three times as fast as the analogous reaction at the NB/water interface.; A new electrochemical generation/collection (G/C) technique based on the use of dual-pipet electrodes was developed for studying heterogeneous IT reactions and homogeneous chemical reactions involving ionic species. This technique allows quantitative separation of different charge transfer processes simultaneously occurring at the liquid/liquid interface. Using a dual-pipet device one can perform measurements in a thin liquid film formed on the surface of glass separating two barrels. In this way, voltammetry can be carried out “in the air”, i.e., in the absence of the external liquid macrophase.; SECM was used to probe the redox activity of individual living cells. The possibilities of measuring the rate and investigating the pathway of transmembrane charge transfer are demonstrated. By this approach, the differences in the redox responses given by normal human breast epithelial cells and metastatic breast cancer cells were investigated. The correlation between redox activity and cellular metastasis was explored. Finally, the amperometric feedback and potentiometric modes of SECM were used to image the topography and map redox and acid-base activities in single mammalian cells.