Figure 1
Staining of E. coli with a safranin dye solution. (a) An E. coli suspension (0.5 mL) separated into the supernatant and bacterial cells by centrifugation. (b) E. coli cells were taken, and 0.5 mL normal saline solution was added to the cells. (c) E. coli cells in saline solution were stained with a droplet of safranin dye solution. (d) Stained cells and safranin dye solution were separated by centrifugation. (e) The stained bacterial cells were dissolved in saline solution at a density of 104 CFU/mL. (f) Optical absorption spectrum (absorbance) of an unstained E. coli solution (blue line), a safranin dye-stained E. coli solution (red line), and a rhodamine B dye-stained E. coli solution (orange line). The absorbance of E. coli at 532 nm was 0.084 for an unstained sample, 0.2 for a safranin-stained sample, and 0.38 for a rhodamine B-stained sample. (g) Theoretical plot of a temperature rise of a dye-stained E. coli as a function of time for pulsed (blue line) or CW (red line) laser irradiation. Inset shows schematic diagram of the thermal inactivation of E. coli by laser irradiation (green arrows), where the laser beam is efficiently absorbed by safranin- or rhodamine B dye-stained E. coli. Energy dissipation due to thermal convection is indicated by dashed arrows.
