Biosynthesis Of Silver Nanoparticles Using Bletilla Striata Extract And Its Biological Activities

Plant reduction method is one of the important methods to prepare silver nanoparticles by biological method,and it is a widely recognized green synthesis method at present.Bletilla striata is a perennial herb of the genus Bletilla of Orchidaceae,which is mainly distributed in most areas south of Qinling Mountains and Huaihe River in China.B.striata is mainly used in the treatment of lung injury,hemoptysis,bleeding,carbuncle,ulcer pain and other symptoms.at present,there is no research report on the preparation of nano-silver as a reducing agent and protective agent.As a new type of efficient fungicide,silver nanoparticles have the advantages of high safety,good stability,broad-spectrum bactericidal and not easy to produce drug resistance,so they are widely used in many fields,especially in the field of biomedicine.In order to further develop the medicinal value of B.striata,the extract of B.striata was used for reducing agent and protective agent to prepare silver nanoparticles.The properties of the prepared silver nanoparticles were studied.The main research contents are as follows:(1)The extract of B.striata was prepared by ultrasonic water extraction and used as reducing agent and protective agent to prepare silver nanoparticles(BS-AgNPs).The effects of preparation conditions such as the amount of B.striata extract,silver nitrate concentration,reaction time and reaction temperature on the yield of BS-AgNPs were studied.The preparation conditions of BS-AgNPs were optimized by single factor method and response surface method.The optimum preparation conditions of BS-AgNPs were determined as follows:the amount of B.striata extract 28.6 mL,silver nitrate solubility3.9 mmol/L,reaction time 2.1 h,reaction temperature 87 ℃(the total system is 50 mL).The obtained BS-AgNPs is golden yellow and has an obvious characteristic absorption peak of nano-silver at 431 nm.The particle size of BS-AgNPs particles ranges from45.71 to 121.89 nm,the average particle size is 81.7 nm,the particle size shows a normal distribution,and the dispersion is good.Scanning electron microscope(SEM)images showed that BS-AgNPs was nearly spherical.(2)BS-AgNPs has excellent antibacterial activity against Escherichia coli,Staphylococcus aureus and Bacillus subtilis,among which Bacillus subtilis is the most sensitive to BSAgNPs.The minimum inhibitory concentration(MIC)of BSAgNPs to E.coli,S.aureus and B.subtilis were 0.90 μg/mL,3.59 μg/mL and 0.45 μg/mL,The minimum bactericidal concentration(MBC),3.59 μg/mL,14.38 μg/mL and 1.80 μg/mL,respectively.The bacteriostatic kinetic experiments were carried out with MIC and MBC as reference concentrations.The results showed that BS-AgNPs could effectively inhibit the growth of E.coli,S.aureus and B.subtilis.The bacteriostatic circle test of E.coli,S.aureus and B.subtilis was carried out with the same concentration of BS-AgNPs,silver nitrate and Ampicillin(Amp).The results showed that BS-AgNPs had better antibacterial activity than Amp on E.coli,S.aureus and B.subtilis.(3)BS-AgNPs has certain scavenging ability to DPPH free radical and ABTS free radical.When the concentration of BSAgNPs is 0.35 mg/mL,the scavenging rate of DPPH free radical reaches 69.32%;when the concentration of BS-AgNPs is 40mg/L,the scavenging rate of ABTS free radical reaches 91.31%.In addition,the total antioxidant capacity of BS-AgNPs was also studied.when the concentration of BS-AgNPs reached 0.5mg/mL,the maximum total antioxidant capacity of BS-AgNPs was about 21.60% of that of pure antioxidant Vitamin C(Vc)at the same concentration.The results showed that BS-AgNPs could also effectively scavenge DPPH free radical and ABTS free radical at low concentration,and the scavenging ability to ABTS free radical was stronger.(4)Using polyvinyl alcohol(PVA)and BS-AgNPs as raw materials,BS-AgNPs hydrogel dressing was prepared by freezing-thawing method.Related experiments show that BSAgNPs hydrogel has the following advantages:(1)good light transmittance,which is easy to observe wound healing;(2)water absorption of about 91.5%,which can effectively maintain the moist environment of the wound and promote wound healing;(3)has a good bacteriostatic effect on the growth of both Grampositive bacteria and Gram-negative bacteria.