ABSTRACT
Heterogeneous charge transfer (CT) reactions at the interface between two immiscible electrolyte solutions (ITIES), i.e., electron transfer (ET), and simple and facilitated ion transfers (IT), are of fundamental importance for many biological and technological systems. During the last two decades, electrochemical methods have been extensively used to probe the thermodynamics and kinetics of these processes [1]. The charge transfer rates at the ITIES are often very fast and hard to measure. Measurements of fast kinetics at larger ITIES are prone to errors due to the uncompensated resistive drop (iR-drop) and charging current. In 1986, Taylor and Girault introduced a micrometer-sized liquid-liquid interface supported at the tip of a pulled glass micropipette [2]. Later, Girault's group developed another approach to micro-ITIES fabrication by making a microhole in a thin inert membrane using a UV laser photoablation technique [3a]. While the shape of a micropipette and the small size of its tip are most suitable for sensor applications (see Sections IV.D and IV.E below), the higher symmetry of a microhole simplifies theoretical analysis of steady-state voltammetric measurements.
