Dynamics of single biomolecules in free solution.

Instrumental advances have allowed the continuous observation of single-molecule trajectories in free solution. Diffraction-limited spectral resolution at video frame rates is routinely achieved by using commercial, intensified, charge-coupled device cameras, low-power continuous-wave lasers, and standard optical microscopes. Either the native fluorescence from large biomolecules or emission from conjugated fluorescence labels can be employed to follow multiple molecules over many seconds. Both molecular motion at the liquid/solid interface and in bulk solution can be recorded. The former reveals adsorption and desorption probabilities that are related to chromatographic retention processes and to the applicability of biocompatible materials. The latter allows the manipulation of particles and large biomolecules to facilitate separation and identification.