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Reactive oxygen species (Apex, N.C.)

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Our early work suggested that graphene quantum dots (GQDs) block Cu(II)/Cu(I) redox cycle in biological systems. Here we report that GQDs could also potently protect against copper redox-mediated oxidative DNA damage. Using Cu(II)/hydrogen peroxide, Cu(II)/hydroquinone, and Cu(II)/ascorbic acid as three biologically relevant systems for inducing oxidative DNA damage, we demonstrated that GQDs protected against the above system-induced DNA strand breaks in ϕx-174 plasmid DNA in a concentration-dependent manner. Notably, a significant protection was observed with GQDs at 1 μg/ml, and a nearly complete protection was shown with 10 and 100 μg/ml of GQDs. Using electron paramagnetic resonance (EPR) spectrometry in conjunction with α-(4-pyridyl-1-oxide)--tert-butylnitrone (POBN)-spin trapping, we showed that the above three systems generated hydroxyl radicals, as evidenced by the formation of a POBN-CH radical adduct in the presence of 0.5 M dimethyl sulfoxide (DMSO). Consistent with the protective effects of GQDs on DNA damage, the hydroxyl radical formation was markedly reduced in the presence of GQDs in a concentration dependent manner. A nearly complete blockage of the hydroxyl radical generation was seen with GQDs at 10 and 100 μg/ml. Taken together, our results showed that GQDs potently protected against oxidative DNA damage. Considering the critical role of copper in cancer development, our findings might have important implications for cancer intervention with GQD-based nanotech modality.