Fig. 4.

Distinct antibacterial activity of Pd nanocrystals. Both Gram-positive and Gram-negative bacteria are tested for the antibacterial activity with Pd nanocrystals. a Survival rates of S. aureus treated with various concentrations of Pd nanocrystals in terms of the number of surface atoms per milliliter. The colony-forming units counting method was applied to evaluate the actual antibacterial effects of the Pd nanocrystals. The data indicate the means and SD from three parallel experiments. b Typical SEM images of the S. aureus cells exposed to various treatments. Scale bar: 1 μm. c Representative fluorescence images of live (green) and dead (red) cells. Scale bar: 10 μm. d Quantitative analysis of the ROS levels in S. aureus cells after different treatments. The data indicate the mean fluorescence intensity and SD from three regions. P-values were calculated by the student’s test: *p < 0.05. e Survival rates of E. coli treated with various concentrations of the Pd nanocrystals in terms of the number of surface atoms per milliliter. The data indicate the means and SD from three parallel experiments. f Typical SEM images of E. coli cells exposed to various treatments. Scale bar: 1 μm