Different anisotropic silver nanocrystals show different antibacterial activities- an effect of different prominent crystallographic orientations in different shapes

The antibacterial activity of silver (Ag) nanoparticles is well established and various researchers have provided different explanations for the same. We have tested the activity of similar-sized anisotropic Ag nanocrystals. Silver nanocubes and nanohexagons were prepared and their antibacterial activity was tested against a few bacteria such as Bacillus cereus, Escherichia coli, Salmonella typhi, Staphylococcus epidermidis, Klebsiella pneumonia, Vibrio parahaemolyticus and Pseudomonas aeruginosa. It was found that the two shapes were active against all these bacteria. However, the plot of cell density of different bacterial pathogens against the concentration of silver nano-crystals was found to be different for these two shapes. Moreover, half maximal inhibitory concentration value and minimum bactericidal concentration value were also different for the two shapes. XRD analysis showed that both the nanocrystals were crystalline in nature, but their crystallographic orientation was different. So, it can be inferred from this study that some crystallographic planes are probably more active towards reaction with different bacterial compositions and hence, responsible for stronger antibacterial activity. (author)