Stabilization of (CdSe)ZnS quantum dots in water using amino acid capping groups

We report investigations of the binding of amino acids to the surface of colloidal quantum dots that comprise a cadmium selenide core, with a zinc sulfide shell, (CdSe)ZnS. The goal of this work is to replace the TOP/TOPO capping group, created during synthesis, with amino acids that can confer solubility of the quantum dot in a buffered aqueous environment, while retaining or improving the good electronic properties of the quantum dot Steady-state and time-resolved photoluminescence studies, combined with quantum chemical calculations are used to explain the relative efficiency of three amino acids (histidine, lysine and cysteine) to bind and passivate the quantum dot surface as a function of pH. These results are compared to the more common mercaptopropionic acid that is often used to solubilize these QDs in water.