Surface plasmon resonance (SPR) is a sensitive optical technique used to measure the interaction between molecules. It occurs when light hits a metal surface, causing electrons to oscillate and create surface plasmons. This interaction can be detected as changes in the light's intensity or angle, allowing researchers to study binding events in real-time. SPR is widely used in biotechnology and pharmaceutical research to analyze biomolecular interactions, such as protein-protein or protein-DNA binding. By monitoring these interactions, scientists can gain insights into various biological processes and develop new drugs or therapies.