Enhanced antibacterial activity of decahedral silver nanoparticles

The size and shape of silver nanoparticles (AgNPs) can potentially influence their antibacterial activity. In this study, a photochemical approach was adopted for the synthesis of decahedral AgNPs and their antibacterial activity was tested and compared against that of spherical AgNPs of similar size synthesized using the chemical reduction approach. The UV-vis spectra indicated the synthesis of decahedral AgNPs with a localized surface plasmon resonance (LSPR) peak at 502 nm. The spherical AgNPs exhibited the LSPR peak at 416 nm. Analysis of field emission gun-transmission electron microscopy (FEG-TEM) micrographs demonstrated the average diameter of decahedral silver nanoparticles as 52.1 +/- 5.7 nm with side length as 33.2 +/- 3.1 nm. In contrast, the average size of spherical AgNPs was 44.2 +/- 6.3 nm. The decahedral AgNPs demonstrated ten times higher bactericidal activity as compared to the spherical AgNPs across all the bacterial strains tested. The minimum inhibitory concentration (MIC) for decahedral AgNPs was in the range of 4-8 mu g/ml for all the four bacterial strains tested, whereas, for spherical nanoparticles of comparable size, the MIC was in the range of 40-80 mu g/ml. The minimum bactericidal concentration (MBC) for decahedral AgNPs was in the range of 6-10 mu g/ml. At the same time, spherical AgNPs of comparable size exhibited MBC in the range of 60-100 mu g/ml for the four bacterial strains. In terms of bactericidal effect, Escherichia coli MTCC 443 was found as the most sensitive strain, while in terms of growth inhibition, Bacillus subtilis was the most sensitive strain. Staphylococcus aureus NCIM 5021 was the most resistant among the tested bacterial strains.