Fig. 1. Schematic of optical system for photodynamic therapy

Fig. 2. Characterization of C-dots. (a) Particle size; (b) absorption spectrum; (c) fluorescence spectra; (d) two-photon excited fluorescence; (e) variation curve of characteristic absorption peak (λ＝399 nm) of ABDA under light irradiation with different light irradiation time, where the inset shows UV-Vis spectra of ABDA and C-dots under light irradiation for different time; (f) absorption spectra of C-dots in PBS for different time; (g) absorption spectra of C-dots under light irradiation for different time; (h) assessment of biocompatibility of C-dots

Fig. 3. Fluorescence images, merged images, and bright field images of HeLa cells stained with both RNASelect and C-dots, where excitation and emission wavelengths of C-dots channel are λ_ex＝552 nm and λ_em＝560－590 nm, excitation and emission wavelengths of RNASelect channel are λ_ex＝488 nm and λ_em＝510－540 nm, the concentration of RNASelect is 10 μmol/L, and the mass concentration of C-dots is 500 μg/mL

Fig. 4. Necrosis development in response to nucleolus-targeted two-photon PDT. HeLa cells incubated with/without C-dots were irradiated by two-photon scans with different time, where excitation and emission wavelengths of Calcein channel are λ_ex＝488 nm and λ_em＝505－525 nm, excitation and emission wavelengths of propidium iodide (PI) channel are λ_ex＝532 nm and λ_em＝605－625 nm, and scanned areas are indicated by yellow squares

Table 1. Light dose for two-photon photodynamic therapy