The present invention provides methods, compositions and applications for efficient, site-specific drug delivery using pro-drug complexes comprising therapeutic agents and one or more functional groups (e.g., imaging agents, targeting agents, and trigger agents). In particular, the present invention relates to pro-drug complexes comprising one or more functional groups conjugated with a therapeutic agent (e.g., a chemotherapeutic agent), methods of synthesizing the same, as well as systems and methods utilizing the therapeutic and diagnostic compositions (e.g., in diagnostic and/or therapeutic settings (e.g., for the delivery of therapeutics, imaging, and/or targeting agents (e.g., in disease (e.g., cancer) diagnosis and/or therapy, etc.)).