Chapter 11. Single Entity Electrogenerated Chemiluminescence

Since Democritus’ time, when the existence of small indivisible entities was proposed, scientists have invented tools to study the nanoverse. The study of single entities, whether those entities are single molecules, nanoparticles, or cells, has important implications to fundamental and applied science. Fundamentally, the study of single entities holds the promise of elucidating new truths of nature that are averaged out in ensemble measurements or hidden in complex systems. In terms of applications, the specific detection of a single entity represents the ultimate sensitivity in analysis: a limit of detection of one. A further application is that the hunger to push science to these levels forces one to invent new technologies that are capable of studying single entities or interpret data once thought to be noise. Many of these experiments take advantage of the properties of molecules, such as redox reactivity or electrocatalysis. Here, we review the study of single entities using electrogenerated chemiluminescence (ECL). We will restrict our scope to single small entities, where ‘small’ is fixed at a few tens of microns. We also restrict our discussion to systems were studying a single entity provides information that could not be obtained by an ensemble measurement.