Surface Plasmon Resonance (SPR) is a sensitive optical technique used to study molecular interactions in real-time. It involves the excitation of surface plasmons, which are coherent oscillations of electrons at the interface between a metal and a dielectric material. When light hits the metal surface at a specific angle, it can cause these plasmons to resonate, leading to a measurable change in the reflected light intensity. This method is widely used in biotechnology and pharmaceutical research to monitor binding events, such as protein-protein interactions or antigen-antibody binding. SPR provides valuable information about the kinetics and affinity of these interactions without the need for labeling the molecules involved.