The nanoparticles known as C dots have been studied in humans, marking the first time this type of ultrasmall inorganic particle has made the leap from animal tests to people (Sci. Transl. Med. 2014, DOI: 10.1126/scitranslmed.3009524). C dots, known formally as Cornell dots for the university where they were first developed, consist of silica nanoparticles 6–7 nm in diameter. The nanoparticles encapsulate the fluorescent dye Cy5, which allows researchers to track them using fluorescence methods. The C dots have a coating of polyethylene glycol, which prevents them from getting caught in the liver. The radiolabeled cyclic peptide 124I-cRGDY also decorates the nanoparticle surface. The cyclic peptide targets integrin present in high concentration on certain cancer cells, and iodine-124 can be tracked using positron emission tomography (PET). Researchers led by Michelle S. Bradbury of Sloan Kettering Institute for Cancer Research and Ulrich Wiesner of Cornell University tested the C dots in five patients with terminal melanoma. They found that the particles were not toxic and were excreted intact by the kidneys and bladder, thanks to their small size.