Scheme 1. Illustration of macrophage cellular Trojan Horse strategy to carry polymer based microparticles containing a photochemical precursor of NO (photoNORM) plus upconverting nanoparticles (UCNPs) into a tumor. NIR activation of the photoNORM/UCNP combination releases NO to mediate the tumor environment in order to facilitate various types of therapy as well as providing the opportunity for photoluminescence imaging.