Green Synthesis And Application Of The Gelatin Stabilized Silver Nanoparticles

Nanosilver materials with ultra-small size and high specific surface area have a wide range of applications including catalysis, biomedical imaging, and antibacterial agents. To protect the nanosilver from aggregation, the capping agents are necessary. The nature of the ligands used for capping the particle surface and the metal-ligand interaction can markedly affect their structural and electronic properties. Gelatin was used as the stabilizer to synthesize the silver nanoparticles through etching method and chemical reduced method in the aqueous solution. The structures of these silver nano-materials were characterized.Their applications in the detection of heavy metal ion and anti-bacterial properties were studied.The main work completed in this thesis can be summarized as followings:(1) A facile approach to synthesize stable, high quantum yield (3.5%), fluorescent silver nanoclusters (AgNCs(E)) by using etching method in aqueous solution without organic solvents was described. The formation of AgNCs (average diameter1.5nm) was probed by UV-Vis absorption and fluorescent spectroscopy. The AgNCs(E) have fluorescence lifetimes of4.60and1.36ns.The optimal synthesis condition is at a1:2molar ratio of Ag+to dihydrolipoic acid (DHLA) and pH3.5. It turned out that the AgNCs have excellent stability when kept in the dark at4℃for four months and over a wide pH range.The fluorescent AgNCs can be used for selective detection of Hg2+with a detection limit of4nM. Finally, the conjugation of a-gelatin and lipoic acid was used as the template for the synthesis of AgNCs(R).(2) A green process was adopted to create gelatin-dextran bioconjugate(bG-D70conj). The bG-D70conj was analyzed by o-phthaldialdehyde (OPA). The conjugates were assembled with silver nitrate(80℃, water-bath) reduced by NaBH4and dextran to produce the silver nanoparticles (AgNPs(1), AgNPs(2)). Besides, we used b-gelatin as the template and dextran as reducing agent to synthesize the silver nanoparticles(AgNPs(3)). We found that the AgNPs(1) have good stability and a considerably UV absorption maximum at412nm. The TEM graph showed that the shape of the AgNPs(1) was spherical and their average diameter was20.4nm. The antibacterial properties of silver nanoparticles against the gram-negative bacterium Escherichia coli showed that the minimum inhibitory concentration (MIC) value of the prepared AgNPs(1) was1.5μg/L, that indicated the silver nanoparticles protected by bG-D7oconj have excellent antibacterial properties.