Further reading:
V. Vaijayanthimala, P.-Y. Cheng, S.-H. Yeh, K.-K. Liu, C.-H. Hsiao, J.-I Chao, and H.-C. Chang, "The long-term stability and biocompatibility of fluorescent nanodiamond as an in vivo contrast agent," Biomaterials 33, 7794-7802 (2012).