Fluorescence quantum efficiency of dry Bacillus globigii spores

Fluorescence spectroscopy has been used to measure fluorescence quantum efficiency (QE) of dried Bacillus spores (washed and unwashed) fixed to a quartz substrate. Fluorescence spectra and QE of anthracene in ethanol was used as the standard. We measured the absorption and fluorescence signal of the spores as a function of the number of spores. The absorption was measured from 600 nm to 250 nm using the reflectance in an integrating sphere. The fluorescence spectra were measured using excitation wavelengths at 280, 360 and 400 nm at room temperature. The absorption cross sections for the unwashed spores were 1.3 × 10^-8, 8 × 10-⁹, and 5 × 10 ^-9 mm²/spore at 280, 360 and 400 nm, respectively. The fluorescence QE was 0.13 ± 0.03, 0.33 ± 0.12 and 0.43 ± 0.26 at 280, 360, and 400 nm, respectively. The QE decreased by a factor of 2, 4 and 4 at these same wavelengths after washing and redrying the spores.