Preparation And Photosensitive Properties Of Bacterial Cellulose-Molybdenum Disulfide Based Materials

The overuse or misuse of antibiotics have led to the emergence and spread of multidrug-resistant pathogens.As such,the prevention of pathogenic infections has become an important medical and societal issue,and new antibacterial strategies are urgently required.In recent years,with the development of science and technology,photoassisted therapy,including photodynamic therapy（PDT）and photothermal therapy（PTT）,has rapidly developed into a new antibacterial technology due to its high antibacterial activity,and has garnered widespread attention.As a photocatalyst with visible light response,molybdenum disulfide（MoS₂）has a 2D structure similar to graphene,which has attracted increasing attention for various applications in environmental and biomedical fields because it possesses intriguing optical,electronic,physical,visible-light-driven photocatalytic,and photothermal properites.To the end,this study immobilized the photosensitive agent MoS₂ on bacterial cellulose（BC）to prepare photosensitive materials and assessed its photodynamic,photothermal properties and peroxidase-like catalytic activity.Firstly,using both in situ biosynthesis and dipping methods,we synthesized a novel cationic bacterial cellulose/MoS₂-chitosan（termed BC/MoS₂-CS）composite scaffold.Then,physical characterization（SEM,EDS,XRD,TGA）and chemical characterization（FTIR,Raman）were used to analyze the morphology,physical and chemical properties of the membranes before and after loaded MoS₂ and CS.The types and relative yields of reactive oxygen species（ROS）produced by the composites under illumination were also investigated by substrate oxidation experiment and electron spin resonance spectroscopy（EPR）.The results showed that MoS₂ and chitosan were successfully loaded on bacterial cellulose.Compared with pure BC,the surface of BC/MoS₂ became more compact.The loading of MoS₂ and CS improved the hydrophilicity and thermostability of membrane.Substrate oxidation experiments and EPR tests showed that BC/MoS₂ had good photodynamic properties,and produced a variety of antibacterial reactive oxygen species（ROS）under illumination,including hydroxyl radical（·OH）and superoxide anion radical(O₂^·-)via typeⅠmechanism and singlet oxygen（¹O₂）via type Ⅱ mechanism.Secondly,the photodynamic therapy（PDT）/photothermal therapy（PTT）synergistic antibacterial mechanism was constructed.The photothermal properties and antibacterial activity of BC/MoS₂ and BC/MoS₂-CS was investigated under different illumination（Xenon vs IR lamp）conditions against two model bacteria,Gram-positive S.aureus and Gram-negative E.coli.The reusability and photostability of composites was assessed.The cytotoxicity of the BC/MoS₂-CS material against mammalian L929 cells was also investigated to determine its biocompatibility.The results showed that the composites have good photothermal conversion performance.After 15 min under Xenon lamp and IR lamp illumination,the temperatures of membrane increased to 50+℃and 70+℃,respectively.The BC/MoS₂-CS nanocomposite exhibited excellent antibacterial efficacy,achieving 99.998%and 99.988%photoinactivation of E.coli and S.aureus,respectively,under visible-light illumination（Xenon lamp,500 W,λ≥420 nm,30 min）.Under IR lamp illumination（100 W,760 nm≤λ≤5000 nm,15 min）,the antibacterial efficiency of the two kinds of bacteria reached 99.999%.Mechanistic studies revealed that positively charged chitosan can disrupt the bacterial cell membrane integrity,and the synergistic effect of hyperthermia（photothermal）and reactive oxygen species（photodynamic）lead to the inactivation of pathogens upon visiblelight illumination.After four photoinactivation cycles,the antibacterial efficacy of the membrane against both E.coli and S.aureus was still greater than 90%,demonstrating that the materials are reusable.The photobleaching results suggested that the MoS₂ photosensitizer exhibited reasonably good photostability.Moreover,no mammalian cell cytotoxicity was observed for the BC/MoS₂-CS membrane,suggesting that such composite nanomaterials are attractive as functional materials for infection control applications,especially in the combined field of photodynamic therapy（PDT）and photothermal therapy（PTT）.Finally,based on the peroxisase-like catalytic activity of MoS₂ nanomaterials,BC/MoS₂+H₂O₂ was used to establish an exogenous·OH-enhanced PDT/PTT system.The·OH yields in different systems were analyzed by substrate oxidation experiment and EPR test.The ability of BC/MoS₂ to photodegrade textile dyes,phenols and aldehydes and antibacterial activity against two model bacteria,Gram-positive S.aureus and Gram-negative E.coli in the presence of H₂O₂（0,0.1,1,10,100 mM）was assessed under different illumination conditions.Substrate oxidation experiment and EPR test showed that BC/MoS₂+H₂O₂ enhanced the yield of·OH and the generation of·OH radicals by the BC/MoS₂ membrane was found to be concentration-dependent for H₂O₂ under illumination.Photodegradation experiments showd that upon illumination,the hydroxyl radicals generated by the BC/MoS₂+100 mM H₂O₂ led to a greater degree of photodegradation（in excess of 95%）of malachite green,catechol violet,and formaldehyde and the degradation process followed the rule of quasi-first-grade dynamics.After four photodegradation cycles,the photodegradation efficiency of the membrane was still greater than 75%,which proved that BC/MoS₂ nanocomposite membrane had good reusability,and provided possibility for its application in industrial wastewater purification.In the presence of 100 mM H₂O₂,the BC/MoS₂ nanocomposite exhibited excellent antibacterial efficacy upwards of 99.9999%and 99.8%for the photoinactivation of E.coli and S.aureus,respectively,upon Xenon lamp illumination.Under IR lamp illumination,the antibacterial efficiency of the two kinds of bacteria reached 99.999%.Mechanistic studies revealed the BC/MoS₂ can effectively catalyze H₂O₂ to produce·OH with strong oxidizing property,which degrade various pollutants and induce oxidative stress of bacteria.Additionally,the synergistic effect of ROS and hyperthermia induced by the absorption of IR light via a photothermal process further contributes to the inactivation of the pathogens.The BC/MoS₂+H₂O₂ is expected to be used as bactericidal materials or photocatalysts for infection control and textile wastewater treatment.