CdSe/ZnS core/shell quantum dots as luminescence lifetime sensors for Cu2+

We report the use of CdSe/ZnS core/shell quantum dots QDot800 (Invitrogen) as luminescence lifetime sensors for copper ions Cu2+(H2O)8 in solution with a sensitivity of <1 ppb that is relevant to intracellular copper concentrations. Excitation of QDot800 at 485 nm was found to be optimum in that it did not cause any change in the level of luminescence intensity or luminescence lifetime in the absence of copper ions. When excited at 485 nm a bi-exponential luminescence decay of QDot800 was observed suggesting the presence of two distinct emitting states, both capable of undergoing metal ion quenching that facilitates Cu2+ detection. Selectivity for copper, as against other transition metal ions, as well as other evidence, suggests the primary origin of the quenching is luminescence resonance energy transfer to both free and bound copper ions. The luminescence kinetics of quantum dots and their optimization and applicability for resonance energy transfer-based lifetime sensing in general is discussed.