Electrochemistry to record single events

Even if tracking single electrons in electrochemical systems is still presently not achieved, single events for which there are more than about 1000 electrons transferred can be recorded. Among these, individual redox molecules can be detected provided that redox cycling occurs between two electrodes separated by a nanometric distance. This opens new concepts in (bio)sensing devices. When current flows through nanopores, small objects such as DNA strands induce fluctuations each time they obstruct the hole. These can be recorded with very good temporal resolution for possible future DNA sequencing. If large enough nanoparticles can be electrolysed, or if smaller ones induce electrocatalysis when contacting the electrode, spikes contain a lot of information. In the field of molecular electronics, electrochemistry may be very useful to make devices for contacting single molecules or realising nanostructures. Wether redox molecules are trapped inside a nanogap, the reference electrode can be used as a gate to realise a single-molecule transistor. Finally, when large objects move in the vicinity of an electrode, their distance can be estimated with a nanometric precision through analysis of the current flux variations induced by the movements. Therefore, new avenues are opened in various fields of electrochemical science through experiments on individual systems. Some are described in this review, focussing on the most recent developments.