Figure 4: Dark toxicity in HeLa cells (A) and HUVEC cells (B) of the glutaraldehyde-cross-linked NP, the DSP-cross-linked NP, and the free Ce6 at different drug concentrations after a 24 h incubation. Asterisks indicate statistical significance with *p<0.05, **p<0.001, and ***p<0.0001.