Oxygen-sensitive quantum dots for possible nanoscale oxygen imaging in cultured cells

Quantum dots (QDs) are the semiconductor crystal with a nanometer particle size that emit fluorescence of a size-dependent wavelength. In this study, we examined whether L-cysteine-capped CdTe quantum dots (QD580, diameter ~4 nm) might be used as an optical probe for intracellular oxygen (O2) in cultured cells. QD580 was successfully introduced in cultured COS-7 cells by incubating cells with 10 nM QD580 for 5-60 min at 37°C. Cells were exposed to 20 % O2 (0.5 h), then 0.5 % O2 or 20 % O2 (1 h), and finally 20 % O2 (0.5 h) gases. We found significant increases in the fluorescence intensity at 0.5 % O2. However, when compared with QD580 in buffer solution, QD580 fluorescence in cells was considerably weak and vulnerable to repeated excitation light exposures. The present study demonstrated the potential of L-cysteine-capped CdTe QDs as a nanoscale probe for intracellular O2 in cultured cells. Further improvement of the QD is necessary for quantitative assessment of O2 in the cell.