POD Nanozyme optimized by charge separation engineering for light/pH activated bacteria catalytic/photodynamic therapy

Abstract

The current feasibility of nanocatalysts in clinical anti-infection therapy, especially for drug-resistant bacteria infection is extremely restrained because of the insufficient reactive oxygen generation. Herein, a novel Ag/Bi₂MoO₆ (Ag/BMO) nanozyme optimized by charge separation engineering with photoactivated sustainable peroxidase-mimicking activities and NIR-II photodynamic performance was synthesized by solvothermal reaction and photoreduction. The Ag/BMO nanozyme held satisfactory bactericidal performance against methicillin-resistant Staphylococcus aureus (MRSA) (~99.9%). The excellent antibacterial performance of Ag/BMO NPs was ascribed to the corporation of peroxidase-like activity, NIR-II photodynamic behavior, and acidity-enhanced release of Ag⁺. As revealed by theoretical calculations, the introduction of Ag to BMO made it easier to separate photo-triggered electron-hole pairs for ROS production. And the conduction and valence band potentials of Ag/BMO NPs were favorable for the reduction of O₂ to ·O₂^-. Under 1064 nm laser irradiation, the electron transfer to BMO was beneficial to the reversible change of Mo⁵⁺/Mo⁶⁺, further improving the peroxidase-like catalytic activity and NIR-II photodynamic performance based on the Russell mechanism. In vivo, the Ag/BMO NPs exhibited promising therapeutic effects towards MRSA-infected wounds. This study enriches the nanozyme research and proves that nanozymes can be rationally optimized by charge separation engineering strategy.

Scheme 1

Preparation of Ag/BMO nanozyme and NIR-enhanced catalytic activity mechanisms for synergistic bacterial therapy

Fig. 1

Characterization, Ag+ release, and photo-enhanced ROS generation ability of Ag/BMO. If not otherwise specified, 1064 nm laser (1 W cm⁻², 10 min) was applied in the laser treatment groups and all NPs were dissolved in DI water for detection. a–c SEM, HRTEM, SAED images of Ag/BMO NPs. d UV-vis absorption of BMO and Ag/BMO NPs solution in water. e, f XPS spectra of Mo 3d and Ag 3d. g Doping content of Ag NPs (The concentration of AgNO₃ is ranging from 1 to 15 mg L⁻¹). h Percentage release of Ag⁺ at pH 7.35 and pH 6.75. i The ¹O₂ detection using SOSG probe. j ESR spectra of ¹O₂. k The ·OH detection using MB indicator. I ESR spectra of ·OH

Fig. 2

Density functional theory theoretical calculations of Ag/BMO nanozyme. a Bader charge of Ag, BMO, and Ag/BMO. b, c Differential charge density and plane-averaged electron density difference along the z-axis of Ag/BMO. The isosurface is 0.002 eV/ų. The yellow and gray color represents gain and lost electrons, respectively. d CB and VB configurations of Ag, BMO, and Ag/BMO

Fig. 3

In vitro antibacterial performance of Ag/BMO nanozyme. 1064 nm laser: 1 W cm⁻² for 10 min, H₂O₂: 3 mM, Ag/BMO NPs: 200 μg mL⁻¹. If not otherwise specified, all NPs were dissolved in DI water for detection. a Plate photographs demonstrating the antibacterial activity of Ag/BMO NPs. b Corresponding quantitive survival ratio of MRSA in (a). c Bacteria viability by monitoring absorbance change at 600 nm (The concentration of NPs solution ranged from 0 to 1024 μg mL⁻¹). d CLSM images of MRSA stained by LIVE/DEAD dye following incubation with Ag/BMO NPs with or without NIR laser irradiation. (PI emits red fluorescence and SYTO9 emits green fluorescence). e, f Fluorescence images and the corresponding quantified analysis result using DCFH-DA fluorescent probe

Fig. 4

In vivo MRSA-infected wound healing effect of Ag/BMO nanozyme. 1064 nm laser: 1 W cm⁻² for 10 min, H₂O₂: 3 mM, Ag/BMO NPs: 200 μg mL⁻¹. If not otherwise specified, all NPs were dissolved in DI water for detection. a The change of wound areas for 7 d. P-value indicates the significant difference. **P < 0.01, ***P < 0.001. b, c Photographs of MRSA-infected wounds in various groups and the corresponding plates after treatments. Scar bar: 1 mm. d The quantified data of survival MRSA in infected wounds treated with different groups. P-value indicates the significant difference. **P < 0.01, ***P < 0.001. e ROS level of infected wounds (more red fluorescence indicated more ROS content). f H&E and Masson-stained tissues slices of infected wounds. g The percentage number of neutrophils and collagen index. h Levels of IL-6 and TNF-α. i Blood biochemistry and physiological index analysis for control and Ag/BMO groups