Provided are compositions and methods for transport, monitoring the transport, and controlled release of active agents. The compositions comprise surface functionalized iron oxide nanoparticles. The iron oxide nanoparticles are surface functionalized with cucurbitril[7] macrocycles. The cavity formed by the CB[7] macrocycles can be used for storage and transport of active agents. The active agents may be imaging agents or may be therapeutic agents which can be released by applying an alternating magnetic field at desired locations.
