Oxygen-Sensitive Quantum Dots for Possible Nanoscale Oxygen Imaging in Cultured Cells

Abstract

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.