Single-particle tracking

Single-particle tracking (SPT) is the observation of the motion of individual particles within a medium. The coordinates time series, which can be either in two dimensions (x, y) or in three dimensions (x, y, z), is referred to as a trajectory. The trajectory is typically analyzed using statistical methods to extract information about the underlying dynamics of the particle. These dynamics can reveal information about the type of transport being observed (e.g., thermal or active), the medium where the particle is moving, and interactions with other particles. In the case of random motion, trajectory analysis can be used to measure the diffusion coefficient. Single-particle tracking (SPT) is the observation of the motion of individual particles within a medium. The coordinates time series, which can be either in two dimensions (x, y) or in three dimensions (x, y, z), is referred to as a trajectory. The trajectory is typically analyzed using statistical methods to extract information about the underlying dynamics of the particle. These dynamics can reveal information about the type of transport being observed (e.g., thermal or active), the medium where the particle is moving, and interactions with other particles. In the case of random motion, trajectory analysis can be used to measure the diffusion coefficient. In life sciences, single-particle tracking is broadly used to quantify the dynamics of molecules. Furthermore, exogenous particles are employed as probes to assess the mechanical properties of the medium, a technique known as passive microrheology. This technique has been applied to investigate the motion of lipids and proteins within membranes, molecules in the nucleus and cytoplasm, organelles and molecules therein, lipid granules, vesicles, and particles introduced in the cytosplasm or the nucleus. Additionally, single-particle tracking has been extensively used in the study of reconstituted lipid bilayers, intermittent diffusion between 3D and either 2D (e.g., a membrane) or 1D (e.g., a DNA polymer) phases, and synthetic entangled actin networks. The most common type of particles used in single particle tracking are based either on scatterers, such as polystyrene beads or gold nanoparticles that can be tracked using bright field illumination, or fluorescent particles. For fluorescent tags, there are many different options with their own advantages and disadvantages, including quantum dots, fluorescent proteins, organic fluorophores, and cyanine dyes.