NQO1 and neoplasm: The resulting dHA-Azo-Ce6 is expected to efficiently penetrate the tumor tissue, and the Azo linker would be degraded by nicotinamide adenine dinucleotide phosphate (NADPH) and azo-reductase, which are abundant in the hypoxia condition [6,9], finally producing free photoactive/tumor-toxic Ce6 from the dots (Figure 1a).