Probing molecular interactions is critical for screening drugs, detecting pollutants, and understanding biological processes at the molecular level, but these interactions are difficult to detect, especially for small molecules. A label-free optical imaging technology that can detect molecule binding kinetics is presented, in which free-moving particles are driven into oscillations with an alternating electrical field and the interferometric scattering patterns of the particles are imaged via an optical imaging method. By tracking the charge-sensitive variations in the oscillation amplitude with sub-nanometer precision, the small molecules and metal ions binding to the surface as well as protein-protein binding kinetics were measured. The capability of the label-free measurement of molecular interactions can provide a promising platform for screening small-molecule drugs, probing conformational changes in proteins, and detecting environmental pollutants.