The synthesis, in vitro, and in vivo behavior of tumor‐homing magnetic nanoworms (NW) are described. The particles consist of a chainlike aggregation of iron oxide (IO) cores in a dextran coating. When conjugated with a tumor‐targeting peptide, they interact more effectively with a tumor‐based target in vitro relative to spherical nanoparticles. Untargeted NW display similar in vivo circulation times and enhanced passive accumulation in mouse xenograft tumors relative to untargeted spherical IO nanoparticles.

Fluorescence imaging is one of the most versatile and widely used visualization methods in biomedical research. However, tissue autofluorescence is a major obstacle confounding interpretation of in vivo fluorescence images. The unusually long emission lifetime (5–13 μs) of photoluminescent porous silicon nanoparticles can allow the time-gated imaging of tissues in vivo, completely eliminating shorter-lived (50-fold in vitro and by >20-fold in vivo when imaging porous silicon nanoparticles. Time-gated imaging of porous silicon nanoparticles accumulated in a human ovarian cancer xenograft following intravenous injection is demonstrated in a live mouse. The potential for multiplexing of images in the time domain by using separate porous silicon nanoparticles engineered with different excited state lifetimes is discussed.