Single molecule detection in single living cells

The ability to detect a single analyte molecule represents the ultimate in sensitivity. Single molecule detection has emerged as a powerful tool to characterize heterogeneous systems, in which traditional bulk sampling methods provide a signal averaged over a large number of analytes. Traditionally, single molecule measurements have required highly controlled experimental conditions using ultrapure solvents to create a minimum level of interference. These constraints have primarily limited this technique to examination of systems in vitro. In this report we present the first instance of real-time single molecule detection in living cells. Our experimental approach allows dynamic monitoring of individual fluorophores in vivo, despite the highly complex cellular environment.