Kobayashi, H., Kosaka, N., Ogawa, M., Morgan, N.Y., Smith, P.D., Murray, C. B., Ye, X., Collins, J., Kumar, A.G., Bell, H., Choyke, P.L. In vivo multiple color lymphatic imaging using upconverting nanocrystals. J. Mater. Chem. 2009, 19, 6481-6484.