Nanoelectrochemistry at Liquid/Liquid Interfaces and Biomembranes

Francois Laforge

The electrical and chemical properties of liquid/liquid interfaces (e.g., water/oil) and biomembranes control the behavior of a variety of biological and technical systems. Electrochemistry is a powerful technique for the study of charge transfer at the liquid/liquid interface. Several experimental problems are inherent to large liquid/liquid interfaces (e.g., resistive drop, charging current). Reducing the size of the liquid/liquid interface has been one way to overcome these limitations. In the present work Micropipette and SECM techniques were used to investigate various liquid/liquid micro-to nanointerfaces and biomembranes. Electron transfer at the water/ionic liquid interface has been studied for the first time using the scanning electrochemical microscope. The heterogeneous rate constant of electron transfer between aqueous ferricyanide and ionic liquid-dissolved ferrocene was found to be kf = 0.33 cm/M/s. The partition coefficient of redox species between ionic liquid and water can be determined from short-range SECM current-distance curves under quasi-steady-state conditions. Our investigations on the electrically driven ion transfer between water to neat organic solvent using nanopipettes showed that there are essentially two types of ion transfer behaviors: the transfer of hydrophobic ions which is a one-step process, and the transfers of hydrophilic ions which must be facilitated by hydrophobic organic counterions. Also by studying the role of water dissolved in the organic phase, we conclude that strongly hydrophilic ions are transferred from the aqueous phase to water clusters dispersed in the organic phase. A new device useful for living cell microinjection and more has been developed and tested. The device, called electrochemical attosyringe, can be used to inject precise doses of liquids- from attoliters to nanoliters. Nanoelectrodes are capable of probing regions of space with volumes several microns-cube. This quality renders them useful for spacially resolved studies of intracellular redox reactions. Nanoelectrodes were prepared, characterized and used to probe redox reaction inside living cells, to study molecular transport across the membrane and to image cells.