A nanoparticle size series for in vivo fluorescence imaging.

Any design of nanoparticle vectors for cancer therapy or imaging must take into account the interaction of the nanoparticles with the tumor microenvironment. Size, charge, and shape have been shown to dominate this interaction.[1, 2] In vivo probing of solid tumors with particles of different sizes simultaneously has thus far been challenging due to the limitations of available nano-sized probes.[3–5] Fluorescent dextrans and other macromolecule probes have been used in studies with intravital microscopy, but heterogeneities across samples has prevented their use for the simultaneous imaging of a size series of probes within the same tumour.[5] MRI contrast agents are another attractive set of probes due to the minimally-invasive nature of the technology,[6, 7] but the lower spatial resolution of MRI limits the imaging of heterogeneity within tumors, and the technique does not allow for simultaneous imaging and tracking of a size series of probes within the same tumor.