Then, the cytotoxicity of TPA-H was assessed by CCK-8 assay in HeLa cells. As illustrated in Figure , the viability of HeLa cells is higher than 80% after incubation in 10 μM of TPA-H for 24 h under dark state, implying their good biocompatibility. Upon the white light illuminating for 10 min, only 8.6% of cell viability remained in the presence of 10 μM of TPA-H. The photostability of TPA-H and Mito-Tracker Green were evaluated in HeLa cells (Figures 4B and Figure ). Through continuous laser irradiation, the PL intensity of the HeLa cells stained by TPA-H presented minor change under confocal microscope after illuminating for 3 min, revealing the good photostabilities. As a control, the PL intensity of Mito-Tracker Green distinctly reduced under the same condition (Figure ). As depicted in Figure , TPA-H was used to stain HeLa cells under different incubation time. After staining with TPA-H (2 μM) for 10 min, bright red fluorescence (λem = 600-700 nm) was observed on cell membrane. Surprisingly, when extending the illumination time, TPA-H gradually migrated to other organelle in cell (Figure ). To confirm the specific location, co-localization experiments were conducted with TPA-H and commercial Mito-tracker green (mitochondria staining dye). The red fluorescence of TPA-H was mainly located on cell membrane at the initial stage with a low Pearson's correlation coefficient (PC). Upon prolonging the incubation time to 2, 6 and 9 h, the co-localization with Mitotracker green has an increased PC from 0.31 to 0.52 to 0.74 to 0.86, demonstrating TPA-H gradually translocated from cell membrane to mitochondria. This in situ real-time visualizing fluorescence migration in cells is beneficial to understand PDT process. Moreover, the live/dead cell co-staining assay further supported the PDT properties of TPA-H in the presence of Calcein-AM and propidium iodide (PI). Calcein-AM emits green fluorescence for live cells detection and PI shows red fluorescence in dead cells. When the HeLa cells were incubated with 2.5 µM of TPA-H, bright green fluorescence and slight red emission was were observed under light irradiation (Figure ). Upon increasing the concentration to 10 µM, the green fluorescence totally disappeared and all cells exhibited strong red fluorescence, indicating the high PDT activity of TPA-H. We next demonstrated the PDT ability of TPA-H⊂SAC4A nanoparticles in hypoxic microenvironment. SAC4A showed good biocompatibility no matter in hypoxia or normoxia condition with/without light illumination (Figure ). The supramolecular assemblies also afforded high cell viability in the dark state with or without oxygen supply (Figure ), meaning no PDT was triggered off. When TPA-H⊂SAC4A nanoparticles were incubated in HeLa cells with normal O2 condition under light irradiation, obvious cell killing was obtained with increasing the nanoparticle concentrations. As above-mentioned, TPA-H⊂SAC4A assemblies can drastically inhibit 1 O2 generation, but still produce a small quantity of O2 •-. Therefore, it can kill HeLa cells through PDT. In contrast, when they were incubated in hypoxia under illumination, the cell viability largely decreased, indicating TPA-H can be released from the cavity by decomposition of SAC4A to generate efficient ROS to ablate HeLa cells. Moreover, the live/dead cell co-staining assay was carried out to explore the PDT properties of TPA-H⊂SAC4A under hypoxia or normoxia in the presence of Calcein-AM and PI. As depicted in Figure , when HeLa cells were incubated with TPA-H⊂SAC4A in normoxia condition, bright green fluorescence and small red emission were observed under light irradiation. Upon reducing O2 concentration to 0.1%, strong red fluorescence was attained, indicating many cells were killed by PDT of TPA-H. Thus, we successfully constructed a hypoxia-responsive supramolecular phototheranostic system. In consideration of the efficient cell killing effect of TPA-H, we further explored whether TPA-H treatment will destroy the cell cycle. In this experiment, HeLa cells were treated with TPA-H for 30 min under light irradiation and then determined by flow cytometry. It was worth noting that there occurred S phase accumulation with the increasing concentration of TPA-H (Figure ). In addition, CDK-2, Cyclin A2, P21 and P53 are important modulators for the cell cycle S phase. Western blot analysis manifested that TPA-H treatment resulted in CDK-2 and Cyclin A2 protein downregulation, while P21 and P53 expressions were significantly improved (Figure ). Of note, P21 is cyclin-dependent kinase inhibitor and P53 is tumor suppressor protein. Above results demonstrated that TPA-H may prevent HeLa cell propagation arising from cell cycle S arrest. The good performance of TPA-H and TPA-H⊂SAC4A nanoparticles in cell experiments motivated us to further study in vivo hypoxia-responsive behaviors involving HeLa tumorbearing BALB/c nude mice model. After intratumoral injection of TPA-H (100 μL, 1 mg mL -1 ), the tumor site can be evidently observed strong fluorescence signals at 1 to 48 h, demonstrating its excellent tumor retention property (Figure ). In contrast, no fluorescence signals were detected at the initial stage after injection of TPA-H⊂SAC4A nanoparticles (Figure ). When prolonging the time to 12 h, obvious fluorescence was observed in the tumor site. This is because SAC4A was gradually decomposed in hypoxic tumors and released the included TPA-H to image the tumor tissues. Then, tumors and heart, liver, spleen, lung, kidney were collected to test their fluorescence intensities (Figure ). Intense fluorescence signals were detected in tumor site, but almost no fluorescence signals were obtained in the main organs, which validated the prominent specificity and sustained tumor imaging ability.