text: Despite their potential for use as contrast agents for medical imaging techniques, their use in vivo is hindered by the cytotoxicity of cadmium. To address this issue, methods have been developed to “wrap” or “encapsulate” potentially-toxic QDs in bio-inert polymers to facilitate use in living tissue. While Cd-free QDs are commercially available, they are unsuitable for use as a substitute for organic contrasts. Another issue with CdSe(ZnS) nanoparticles is significant hydrophobicity, which hinders their ability to enter solution with aqueous media, such as blood or spinal fluid. Certain hydrophilic polymers could be used to render the dots water-soluble.