Influence of saline media on the fluorescence emission of Bacillus spores

Single-particle levitation in conjunction with 264.3-nm laser excitation is used to measure the fluorescence emission of individual particles of Bacil lus globigii spores. With precise humidity control, the fluorescence emissi on of wetted and desiccated Bacillus spore particles is measured from 300 t o 450 nm. Comparison of spectra for Bacillus spores suspended in a standard buffer aqueous solution and for a desiccated 10-mu m-diameter aggregate Ba cillus spore particle shows that the spectra is virtually indistinguishable . However, at 85% relative humidity, corresponding to a 4.5M sodium chlorid e solution, the spore spectra redshifts by approximately 25 nm. It is postu lated that the spectra redshifting is a result of specific interactions bet ween the tyrosine fluorophore of the Bacillus spore and the phosphate moiet ies in the buffer solution. (C) 1999 Optical Society of America.