A Metal‐Free Mesoporous Carbon Dots/Silica Hybrid Type I Photosensitizer with Enzyme‐Activity for Synergistic Treatment of Hypoxic Tumor

Abstract

As a less O 2 -dependent photodynamic therapy (PDT), type I PDT is an effective approach to overcome the hypoxia-induced low efficiency against solid tumors. However, the commonly used metal-involved agents suffer from the long-term biosafety concern. Herein, a metal-free type I photosensitizer, N-doped carbon dots/mesoporous silica nanoparticles (NCDs/ MSN, ≈40 nm) nanohybrid with peroxidase (POD)-like activity for synergistic PDT and enzyme-activity treatment, is developed on gram scale via a facile one-pot strategy through mixing carbon source and silica precursor with the assistance of template. Benefiting from the narrow bandgap (1.92 eV) and good charge separation capacity of NCDs/MSN, upon 640 nm light irradiation, the excited electrons in the conduction band can effectively generate O 2 •− by reduction of dissolved O 2 via a one-electron transfer process even under hypoxic conditions, inducing apoptosis of tumor cells. Moreover, the photoinduced O 2 •− can partially transform into more toxic • OH through a two-electron reduction. Moreover, the POD-like activity of NCDs/MSN can catalyze the endogenous H 2 O 2 to • OH in the tumor microenvironment, further synergistically ablating 4T1 tumor cells. Therefore, a mass production way to synthesize a novel metal-free type I photosensitizer with enzymemimic activity for synergistic treatment of hypoxic tumors is provided, which exhibits promising clinical translation prospects.

Multiple Strategies Enhance the ROS of Metal–Organic Frameworks for Energy-Efficient Photocatalytic Water Purification and Sterilization

“…The results show that the photocurrent response signal of GXNU-1 – 3 is much stronger than that of H 2 L, which proves that the formation of three-dimensional and porous MOF structures can effectively enhance the charge separation ability under light-driven conditions and further promote the rapid generation of ROS . Electrochemical impedance spectroscopy (EIS) is commonly used to evaluate semiconductor charge-transfer efficiency . As shown in Figure b, compared with the organic ligand H 2 L, the arc radii of the Nyquist circles observed in GXNU-1 – 3 are much smaller, which means that these MOF structures can promote the rapid charge transfer to generate more holes and excitons, thereby enhancing the generation of ROS .…”

“…As shown in Figure b, compared with the organic ligand H 2 L, the arc radii of the Nyquist circles observed in GXNU-1 – 3 are much smaller, which means that these MOF structures can promote the rapid charge transfer to generate more holes and excitons, thereby enhancing the generation of ROS . The energy band gaps ( E g ) of GXNU-1 – 3 are calculated on the basis of the results of UV–vis absorption spectra and according to the Kubelck–Munk (K-M) equation. ,, The results show that their E g values are 2.78, 2.75, and 2.78 eV, respectively (Figure c). Additionally, Mott–Schottky diagrams can be used to determine the conduction band (CB) potential and conductivity type of the semiconductors. , We tested the Mott–Schottky curves of GXNU-1 – 3 under the conditions of 500, 1000, and 1500 Hz, respectively, and obtained their CBs as −0.31, −0.30, and −0.29 V, respectively, after fitting (Figure d–f).…”

“…All in all, the above results indicate that GXNU-1 – 3 can effectively promote oxygen to produce 1 O 2 under light irradiation conditions, and this evidence is also consistent with the EPR results. To further evaluate the photoinduced electron–hole separation, the fluorescence emission spectra of GXNU-1 – 3 in aqueous solution were measured at different excitation wavelengths of 340, 360, 380, 400, and 420 nm . As shown in Figure S10, at the excitation wavelength of 380 nm, GXNU-1 and -2 exhibit strong fluorescence intensity (λ em = 433 nm); at the excitation wavelength of 380 nm, GXNU-3 exhibits strong fluorescence intensity (λ em = 422 nm).…”

“…63 The energy band gaps (E g ) of GXNU-1− 3 are calculated on the basis of the results of UV−vis absorption spectra and according to the Kubelck−Munk (K-M) equation. 62,64,65 The results show that their E g values are 2.78, 2.75, and 2.78 eV, respectively (Figure 4c). Additionally, Mott−Schottky diagrams can be used to determine the conduction band (CB) potential and conductivity type of the semiconductors.…”

“…18 Electrochemical impedance spectroscopy (EIS) is commonly used to evaluate semiconductor chargetransfer efficiency. 62 As shown in Figure 4b, compared with the organic ligand H 2 L, the arc radii of the Nyquist circles observed in GXNU-1−3 are much smaller, which means that these MOF structures can promote the rapid charge transfer to generate more holes and excitons, thereby enhancing the generation of ROS. 63 The energy band gaps (E g ) of GXNU-1− 3 are calculated on the basis of the results of UV−vis absorption spectra and according to the Kubelck−Munk (K-M) equation.…”