Preparation And In Vitro Study Of Antibacterial And Anticancer Activities Of Silver Nanoparticles

Because of their surface effect, quantum size effect and macroscopic quantum tunneling effect and so on, silver nanoparticles (AgNPs) have unique physical, chemical and biological properties. AgNPs are applied in many fields. Because AgNPs with different shapes and sizes would show different properties, it is difficult but important to prepare the uniform AgNPs.Bacterial infection is one kind of serious communicable disease and antibiotics have been considered as the mainstay in treatment. The phenomenon of abuse of antibiotics has become increasingly and it poses a real threat to public health. AgNPs have effective antibacterial and anti-drug resistance properties and they may possibly be an effective drug in infection treatment, but the relationship between morphofogy and antibacterial activity is still not clear. Existing research shows that the top basal plane of triangular nanoplates is a{111} surface, while in case of the rod-like silver nanoparticles, side surfaces are bound by{100} and the ends by{111} facets. Silver nanospheres and nanocubes predominantly have{100} facets. The above nanoparticles have different antibacterial activity, which may result from their different crystal facets. It is still uncertain whether AgNPs with more{111} facets may have better antibacterial effectCancer disease endangers human life and health because of the high incidence and mortality. Chemotherapy, the main conventional treatment strategy, has several limitations including damaging healthy cells, nonspecificity, toxicity of anticancer drugs and drug resistance. With the further study of AgNPs, it is found that AgNPs have favourable anticancer activity, which has a great application prospect in cancer treatment. The side effect of AgNPs limits their further application in medical field.Based on the above three questions, this thesis will be conducted from following three parts:The first part (chapter 2), we prepared AgNPs with different morphology and studied the influencing factors, in order to obtain AgNPs with a satisfactory monodispersity. The main experimental results are as follows:a) We used A seed solution to prepare AgNPs. Different CTAB solution volume could affect the AgNO3 precursor concentration and it would get different dispersive AgNPs. We got nanorods with a reasonable dispersion by adding 15 mL CTAB solution.b) We got silver nanotriangles by using B seed solution. If the nanotriangles are arranged closely in parallel to each other, the solution will show two UV absorbance peaks that is similar to peaks of naonrods. While nanotriangles are arranged loosely, the AgNPs solution displays three UV absorbance peaks.c) We got silver nanotriangles by using B seed solution and the suitable conditions are as follow:The CTAB concentration should in the range of 0.1 M～ 0.035 M; the NaOH concentration should in the range of 9.0 mM～18 mM; the AgNO3 concentration should in the range of 0.18 mM～0.45 mM; the seed concentration should in the range of 0.023 mM～0.0022 mM. Nanotriangles have different sizes and distributions based on their different concentrations.d) We got silver nanotriangles by using B seed solution. The size of nanotriangles preparing prepared with high mole ratio of Vc to AgNO3 (25～40) is smaller than that with low mole ratio of Vc to AgNO3 (5-20).The second part (chapter 3), we compared the antibacterial activity of silver nanospheres, nanorods, nanocubes and nanotriangles, in order to prove whether AgNPs with more{111} facets could display better antibacterial effect. The main experimental results are as follows:a) We prepared four kinds of silver nanoparticles:AgNPs-1, AgNPs-2, AgNPs-3 and AgNPs-4. The main ingredients of AgNPs-1 and AgNPs-2 are nanocubes and nanospheres respectively while AgNPs-3 are the mixture of nanospheres and short nanorods. We had long naorods with associated nanotriangles in AgNPs-4.b) The antibacterial experiment shows that:silver nanoparticles have better antibacterial activity against Gram-positive bacteria (Staphytococcus aureus) and weaker activity against Gram-negative bacteria (Escherichia coli) than (positive contrast drug) ciprofloxacin.c) AgNPs-1 and AgNPs-2 have similar antibacterial activity. Because of their similar particle sizes, there is no significant difference in the interaction between AgNPs and bacteria; Because of their similar{100} facets, AgNPs-1 and AgNPs-2 have similar releasing efficiency of Ag+ions.d) AgNPs-3 and AgNPs-2 display similar antibacterial efficiency. Although short nanorods can release more Ag+ions, their ability to interact with bacteria is weaker than that of nanospheres because of the low surface-to-volume of nanorods. Under Ihe combined effect of these two factors, short nanorods display the similar antibacterial activity with nanospheres.e) AgNPs-4 have the best antibacterial effect in four kinds of silver nanoparticles. The associated nanotriangles not only can release more Ag+ ions because of their {111} facets but also can interact with bacteria moreeasily because of their edges.The third part (chapter 4), we firstly used a-TOS and histidine to modify AgNPs, in order to counteract their side effect while improve their anticancer activity at the same time. The main experimental results are as follows:a) We prepared three kinds of Ag NPs and they have favourable anti-cancer activity on three cancer cell lines (MCF-7, A549, K562 cancer cells).b) The infrared analysis showed that α-TOS interacted with AgNPs through its CH2-O-CH2 group of the cyclic ether in a-TOS modified AgNPs. The modified Ag NPs with high α-TOS concentration kill all MCF-7 cancer cells at experimental concentration and promote the HL7702 cell survival slightly. Modified Ag NPs with low α-TOS concentration display less cytotoxicity on HL7702 than Ag NPs alone but not affect their anti-cancer activity.c) The infrared analysis showed that histidine interacted with AgNPs through its C-N group of the imidazolyl in histidine modified Ag NPs. Modified Ag NPs with histidine display less cytotoxicity on HL7702 cell and have the similar anticancer activity on MCF-7 cell, while compared to Ag NPs alone.