Quantum dot-based turn-on fluorescent probe for imaging intracellular zinc(II) and cadmium(II) ions

Silica-coated, thiol-enriched and zinc-doped CdS quantum dots (SiO₂-S-Zn-CdS QDs) were fabricated by a sol-gel process and used as fluorescent probe for imaging and monitoring of intracellular Cd(II) and Zn(II) in endophytes in the "turn-on" mode. There is a linear relationship between fluorescence intensity and the concentration of Zn(II) in the 3.5 - 23.2 μM concentration range and with a detection limit of 2.0 μM. The probe also responds well to Cd(II) in the 0.3 - 26 μM concentration range and the detection limit is 0.1 μM. Due to its negligible cytotoxicity, fair sensitivity and good photostability, the quantum dot probe presented here is a promising tool for fluorescent imaging of intracellular Zn(II) or Cd(II). [Figure not available: see fulltext.]