Preparation Of Antibacterial Ti³⁺ Self-doped Modified TiO₂ And Study On Cell Stress Response

Nano-semiconductor photodisinfection technology has attracted much attention due to its unique advantages.Among various bactericidal nano-semiconductor photocatalysts,nano-titanium dioxide（TiO₂）and its modified materials have been widely studied as one of the most popular photocatalysts.Besides of good bactericidal properties,nano-TiO₂ and its modified materials have low toxicological properties,good thermal and chemical stability,etc.,and have great application prospects.In this study,series Pd modified TiO₂-based nanomaterials were synthesized by chemical method.The structural components and other properties,the killing effect,biosafety and stability of the materials against food pathogens and crop pathogens were tested.Finally,the stress response of cells in the mechanism of photodisinfection of nano-TiO₂ was discussed.Firstly,palladium-modified trivalent titanium self-doped nano-TiO₂(Pd/Ti³⁺-TiO₂)composites were prepared by chemical reduction method in this paper.Self-doping can reduce the forbidden band width of TiO₂ composites and make them have visible light response ability.The palladium can capture photogenerated electrons,reduce the recombination of photogenerated electron hole pairs,and improve the photocatalytic efficiency of the materials.Through structural and component analysis,we proved that the Pd/Ti³⁺-TiO₂ composites were successfully synthesized.Sterilization results showed that 10⁷ E.coli could be completely killed after 100 min irradiation under visible light.After 150 min,10⁵ cotton wilt pathogens Fusarium oxysporum could be reduced by four orders of magnitude.Fluorescence test and electron spin resonance showed that the composite could produce a strong redox reactive oxygen group after illumination,and the hydroxyl radical and superoxide radical synergistically play a major role in sterilization.Mammalian cell toxicology experiments and cycle sterilization experiments have demonstrated that the synthesized material was a biosafety and stable nanocomposite.Secondly,the self-doped nano-TiO₂ with metal and non-metal co-modification was synthesized by one-step method.In our study,a series of carbon monoxide and palladium co-modified trivalent titanium self-doped modified nano-TiO₂(Pd/CDs/Ti³⁺-TiO₂)composites were synthesized by solvothermal method.Transmission electron microscopy showed that CDs and Pd were modified on the surface of nano-TiO_2.EPR showed that the sample contained trivalent titanium.The bactericidal effect showed that the Pd/CDs/Ti³⁺-TiO₂composites had good disinfection effect on bacteria and fungi spore under visible light.The photocatalytic bactericidal effect of the synthesized composites with 1%Pd content is the best one.After 30 minutes of irradiation under visible light,10⁷ E.coli could be completely killed.After 60 minutes,10⁵ apple ring disease pathogens could also be completely killed.Its bactericidal performance is better than Pd/Ti³⁺-TiO₂.Thus,co-modification with CDs and Pd can improve the photocatalytic efficiency of the composite.Hydroxyl radicals are the main reason for the photodisinfection activity of the materials after the capture agent experiments,followed by superoxide radicals.Mammalian cell toxicology experiments have shown that the synthesized Pd/CDs/Ti³⁺-TiO₂ was also an environmentally friendly composite.Finally,we focus the prokaryotic model organism Escherichia coli K12 as the research object,and studied the stress response of cells before photodisinfection of cells.The stress responses of bacterial cells under photocatalytic activity of modified nano-TiO₂ were studied by RNA-seq method.In order to better reveal the stress responses of bacterial cells under photocatalytic stress of ROS,we performed multiple photocatalytic stress treatments on wild-type strains（WT）to accumulate stress response effects.After manly times of photocatalytic stress treatment,we screened a mutant strain（MT）with morphological characteristics,metabolism changes and also resistance to photocatalytic active oxygen.The results of RNA-seq and other experiments showed that the stress response of WT to TiO₂photocatalytic ROS was significantly enhanced by flagella assembly ability,which significantly improved the escape ability of chemotactic movement.Interestingly,MT’s carbon metabolism,oxidative phosphorylation,and fatty acid degradation were enhanced compared to WT,while its flagella assembly ability and chemotaxis activity decreased significantly.Remarkably,the superoxide radical degradation ability of MT is significantly improved.We confirmed the decrease of MT exercise ability through puncture experiments.The DCFH-DA qualitative and quantitative experiments confirmed that the concentration of superoxide radicals in cells increased under photocatalytic stress,and the degradation of superoxide radicals by MT was stronger than that of WT.We first reported the mutation of E.coli in TiO₂ photocatalytic reactive oxygen species under multiple stresses.The stress response of the mutant strain to photocatalytic reactive oxygen species changed from escape to enhanced superoxide radical degradation,and the mutant strain TiO₂ photocatalytic reactive oxygen species produce resistance.In this paper,two environmentally friendly modified TiO₂ nanomaterials with visible light response were prepared,which provided a potential alternative materials for the control of pathogenic bacteria.At the same time,it makes up for the blank of cell stress reaction research in photocatalytic antibacterial mechanism research,provides a guidance for preventing the emergence of photodisinferction-resistant strains in semiconductor photocatalytic sterilization,and provides theoretical basis for practical application of semiconductor photodisinferction technology.