Generating experimental data for ligand binding to target protein of interest as well as determination of ligand binding affinity (K_d) is essential for drug discovery. SPR is a label-free optical technique that measures interactions in real time. A target of interest (ligand) is immobilized on a thin gold-coated glass chip while a second molecule (analyte) is flowed over the chip. Changes in the refractive index at the gold surface as the analyte binds to and dissociates from the ligand are monitored to generate sensograms, from which k_on, k_off, and K_D can be calculated.