Analysis of Complex Single-Molecule Kinetics: A Protocol for Single-Molecule Interaction Simulations (SMIS).

Single-molecule techniques have transformed molecular biology by enabling direct observation of individual biomolecular events in real time. While single-molecule localization methods have advanced spatial resolution, they lack the temporal resolution needed to capture dynamic interactions. Single-molecule fluorescence resonance energy transfer (smFRET) addresses this gap by revealing transient molecular states often hidden in ensemble measurements. However, extracting reliable kinetic parameters from smFRET data is hindered by noise artifacts, photophysical effects, and the analytical complexity of stochastic state transitions. To address these limitations, Single-Molecule Interaction Simulation (SMIS) provides a robust framework that enables kinetic analysis by simulating molecular transitions and generating interpretable dwell-time distributions. Unlike traditional approaches requiring complex differential equations, SMIS simplifies kinetic modeling and directly addresses challenges in reproducibility. This chapter outlines a comprehensive protocol for implementing SMIS, from defining kinetic schemes to extracting kinetic rate constants by comparing simulation outcomes against experimental data. By integrating SMIS into the analysis workflow, researchers can extract accurate kinetic insights from smFRET experiments, extending their applicability and enhancing the interpretability of single-molecule studies.