Oxidative stress (ROS levels)

Intracellular ROS formation in NHBE cells exposed to QDs was quantified using 5-(and-6)-carboxy-2′,7′-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA, Molecular Probes, Eugene, OR, USA). NHBE cells exposed to Dulbecco’s phosphate buffered saline (DPBS) only served as negative and 100 µmol/L H₂O₂ served as positive controls. QD controls at the highest concentrations were included in wells without cells to determine if QDs induce spontaneous fluorescence of CM-H₂DCFDA. Fluorescence was measured using an excitation wavelength of 490 nm and an emission wavelength of 535 nm every 10 min post exposure for 120 min. Readings beyond 120 min resulted in errant readings due to cell starvation. Experiments were performed in triplicate on three independent occasions. Representative data from the 60 min reading are presented.