System for modifying a target structure which mediates or is associated with a biological activity, including treatment of conditions, disorders, or diseases mediated by or associated with a target structure, such as a virus, cell, subcellular structure or extracellular structure. The system can be used in methods which can be performed by application of an initiation energy to a subject in situ to activate a pharmaceutical agent directly or via an energy modulation agent, optionally in the presence of one or more plasmonics active agents, thus producing an effect on or change to the target structure.