Assaying of Cu2+ with near-infrared l-cysteine-capped CdSeTe/CdS quantum dots and its effect on cell imaging.

Near-infrared (NIR) core-shell CdSeTe/CdS quantum dots (QDs) modified with l-cysteine were synthesized in aqueous solution. The QDs had a special NIR-emitting spectrum, high fluorescence stability and low cytotoxicity. In addition, they exhibited an obvious fluorescence quenching when Cu2+ was present. An NIR nanosensor was prepared for rapidly, sensitively, and selectively determining Cu2+ in solution quantitatively and monitoring the changes in Cu2+ in cells with fluorescence imaging in a semiquantitative way. The linear relationship between the relative fluorescence intensity (F0 /F) and the concentration of Cu2+ from 5.12 × 10-8  M to 2.56 × 10-5  M in solution was observed using an NIR fluorescence spectrophotometer with R2 equal to 0.9958. Moreover, in the experiment with the fluorescence microscope, F0 /F versus the concentration of Cu2+ from 5.00 × 10-8  M to 7.68 × 10-6  M also showed a good linear relationship with R2 equal to 0.9817. Practical water sample ion detecting experiments had good accuracy and recovery rates. Cell experiments showed that the NIR imaging intensity of cells was inversely proportional to the concentration of copper ions, therefore NIR QDs have great potential for detection of metal ions in solution and in cells.