This paper introduces a novel method for monitoring distances between single pairs of gold and silver nanoparticles using plasmon coupling, which is referred to as "plasmon rulers." The authors demonstrate that this technique can be used to study the directed assembly of nanoparticle dimers and the time dynamics of single DNA hybridization events. The plasmon rulers overcome the limitations of traditional Förster Resonance Energy Transfer (FRET) methods, which suffer from low and fluctuating signal intensities and limited observation time due to photobleaching. The plasmon rulers allow for continuous monitoring of separations up to 70 nm for more than 3000 seconds. The authors also discuss the advantages and potential applications of plasmon rulers, including their use in in vitro single molecule experiments and analytical bulk assays. The methods section details the preparation of nanoparticle conjugates, surface immobilization, and solid-phase hybridization experiments, along with the experimental setup and calculations.This paper introduces a novel method for monitoring distances between single pairs of gold and silver nanoparticles using plasmon coupling, which is referred to as "plasmon rulers." The authors demonstrate that this technique can be used to study the directed assembly of nanoparticle dimers and the time dynamics of single DNA hybridization events. The plasmon rulers overcome the limitations of traditional Förster Resonance Energy Transfer (FRET) methods, which suffer from low and fluctuating signal intensities and limited observation time due to photobleaching. The plasmon rulers allow for continuous monitoring of separations up to 70 nm for more than 3000 seconds. The authors also discuss the advantages and potential applications of plasmon rulers, including their use in in vitro single molecule experiments and analytical bulk assays. The methods section details the preparation of nanoparticle conjugates, surface immobilization, and solid-phase hybridization experiments, along with the experimental setup and calculations.