Effect of the size and shape of silver nanoparticles on bacterial growth and metabolism by monitoring optical density and fluorescence intensity

In this study, we demonstrate the antibacterial activity of silver nanoparticles (AgNPs), depending on their size and shape, on green fluorescent protein (GFP)-expressing E. coli, which provides a facile, rapid, and noninvasive monitoring system. By measuring optical density and fluorescence intensity in the recombinant E. coli, we found that smaller sized plate-shaped AgNPs presented higher antibacterial activity than larger sized, cubic and spherical AgNPs. In the case of 10 nm spherical AgNPs, the optical density was detectable at 15 ng/mL after 12 h incubation, but the fluorescence intensity was not. On the other hand, smaller-sized AgNPs showed higher toxicity than plate-shaped AgNPs based on the measurement of the optical density and fluorescence intensity. The combined analysis of optical density and fluorescence intensity may be helpful for understanding the effect of various materials, including nano- and organic materials, on recombinant bacteria.