drug screening and target identification using surface plasmon resonance imaging of a target protein array is provided . the target protein array / spri system is used as parts of a strategy or method for label - free and real - time identification of a target protein or proteins of any inhibitor , agonist or other ligand . methods that allow for rapidly classifying the mechanism of action of any inhibitor , agonist or other ligand ; and for simultaneous identification and purification of an active ingredient of a natural product extract , which acts specifically on a target protein or proteins are provided . techniques that can be used to prioritize inhibitors , agonists or ligands for lead compound development ; to determine the therapeutic index of drug candidates ; to assess the range of target proteins of drugs or drug candidates or lead compounds in organisms ; and to discover novel target proteins of known drugs or known inhibitors are described .