Modeling the detection of transient vesicular exocytotic release from single cells with cylindrical enzymatic nanoelectrodes

Amperometric electrochemical detection has proven to be an important versatile tool for studying transient single exocytotic events in tissues and single cells. Meanwhile, advances in electrode materials and microfabrication have enabled the routine fabrication of submicrometric electrochemical sensors for in vivo or in vitro analysis of single cells or organelles. In this context, cylindrical nanoelectrodes offer important advantages because their sensing elements can be driven across biological membranes or into intercellular clefts while preserving the biological processes being studied. However, their dimensions and curvatures are comparable to those of the releasing vesicles that deliver their stored material into the extracellular environment. The electrochemical currents are then determined not only by the kinetics of biological release, which is the main objective of monitoring, but also by the intricate diffusion patterns of the analytes in the nanoelectrode-cell space and the kinetics of their electrochemical detection. This situation becomes even more complex when the analytes are not directly electroactive on the electrode surface, but require mediation by an enzymatic process, preventing reliance on classical approaches. Consequently, a theoretical model has been developed to determine and quantify the consequences of these limitations on the electrochemical measurement of transient release processes in quantitative and kinetic terms.