A prevailing belief is that trioctylphosphine oxide (TOPO) or trioctylphosphine (TOP), a neutral ligand derived from a common precursor used in the synthesis of CdSe dots, caps the surface of CdSe quantum dots. However, results from recent studies challenge this model. Using NMR, quantum dots have been shown to be nonstoichiometric meaning that the cadmium to selenide ratio is not one to one. CdSe dots have excess cadmium cations on the surface that can form bonds with anionic species such as carboxylate chains. The CdSe quantum dot would be charge unbalanced if TOPO or TOP were indeed the only type of ligand bound to the dot.