Preparation Of Ag/TiO₂ Nanocomposites And Its Antibacterial And Antimite Performance And Mechanism

Nano-Ag is with the characterization of broad-spectrum antibacterial property and plays a dominant role in bio-medical antibacterial material.However,the usage of Ag/Ti O₂ was largely limited due to not only the hard preparation,readily oxidation and polymeration,the high cost of the production,but also due to its high toxicity.To overcome these drawbacks,the development of Ag/Ti O₂ has become a focus research in present.In this study,we utilized anatase titanium dioxide as a photo-catalysis carrier with a high efficient catalytic activity,successfully prepared the nanocomposite of Ag/Ti O₂（ATA）by using photocatalysis reduction method.In this study,photocatalysis was applied to prepare ATA;transmission electron microscope（TEM）and scanning electronic microscope（SEM）were applied to observe the surface morphology of the particle of ATA;energy spectrometry（EDS）was applied to analyze the component of ATA antibacterial;X-ray diffraction analysis（XRD）was applied to analyze the crystal structure of ATA;and ultraviolet-visible spectrophotometer（UV-vis）was applied to analyze the optical property of ATA antibacterial.We also studied the stability of ATA under varies values of p H and the effect of p H value and catalysitc time on photocatalytic reduction rate and the radius of ATA.Automatic growth curvometer was applied to compare MIC of Ag,ATA,and Ti O₂ to seven common pathogenic bacteria and the mechanism of antibacterial of ATA was preliminary explored.We first adopt the method that ATA contact to Dermatophagoides pteronyssinus to study the antimite activity and we also adopt stereo-microscope,SEM,FT-IR,and AFM to characterize the structural change before and after the ATA exposure,and to compare the change of levels of NO,GSH,and MDA of dust mite before and ATA exposure,and to further explored the mechanisms of antimite activity of ATA.The following conclusions were obtained1.Prepared ATA is with smaller nanometer radius,better stability and its MIC to seven aiming bacteria are all below 16 μg/ml;the concentration of Ag among ATA is about 1/2 to 1/3 compared with pure Ag,for which cost of the using of Ag was largely saved.2.Through the study of the mechanism of anti-bacteria,we found that after the 4 hours treatment of ATA,the relative membrane potential of E.coli and S.aureus were significantly decreased,and a more significant decrease of relative membrane potential was observed in parallel with a increase of ATA concentration.Meanwhile,the total level of NO of E.coli and S.aureus was significantly increased after exposure to ATA.3.We first found that ATA contains a strong antimite activity,for which a rate of antimite up to 98% was followed with 24 hours of ATA exposure with a concentration of 30 μg/cm2.Under stereomicroscope we observed the dust mite which was treated with or without ATA and found that the mites treated by ATA appeared a gradual body shrinkage,jaw body depression,closed forefoot acetabulum,distorted surface stripes convex,genital and anal lesions.Though the analysis of AFM,the mites treated with ATA showed by Young’s modulus were decreased by approximately 2/3.Through FT-IR test for dust mite surface chemical structure,it was found that after ATA treatment,the structure of lips of body wall,the protein and the polysaccharide were changed.It was found that the organelles of mitochondria,endoplasmic reticulum and other endoplasmic reticulum were destroyed after ATA treatment,and a lot of vacuoles appeared,which also explained the morphological changes and the Young’s modulus s reason.Moreover,we found that in ATA treated dust mite,compared with control,the level of lipid oxidation was slightly increased,and the concentration of NO was increased by 116%,whereas GSH was decreased dramatically to 28.5%,which suggested that the death of dust mite treated with ATA might due to the increased level of toxic NO but decreased level of de-toxic GSH.4.Cytotoxicity experiment,hemolytic test and murine acute toxicity test were used to study the biocompatibility of the nanometer material of ATA.It was found that after treatment with 8 μg/ml ATA to murine fibroblast for 24 hours,cell livability was approximately 80%;when the same concentration of pure Ag was treated,the cells were almost all dead,which indicate ATA,which is mixed with Ag and Ti O₂,dramatically decreased the toxicity of Ag.Hemolytic test showed that followed with the increase of the concentration of ATA,the hemolysis was synergistically increased;however,when the concentration of ATA was below 24 μg/ml,the hemolysis was continuously less than 5% and the RBC kept the normal shape.This result indicates that ATA do not induce hemolysis in regular use.Moreover,gavage administration to Balb/c mice with ATA at doses as high as 600 mg/kg did not induce abnormal behavior nor death,and the body weight is also normal.Non pathogenic nor inflammatory tissue were observed in the mouse by using histological section of heart,liver,spleen,lung,kidney,stomach,and intestine,which indicated ATA is a relatively safe and reliable antibacterial material.