Determination of spectral fluorescence cross sections of bacteria aerosols: Achievements, challenges, and limitations

Kurzfassung

Spectral fluorescence cross sections of bacteria provide information on the distinguishability of bacterial species using fluorescence spectroscopy. A database of cross sections supports the evaluation of spectra achieved by optical detectors based on laser induced fluorescence. Furthermore, the dataset facilitates the selection of surrogates for pathogens in test environments by verifying similar fluorescent properties. The derivation of cross section data from measured fluorescence spectra necessitates the absolute calibration of the measuring system. In the presented device, the fluorescence is measured in a highly diluted aerosol flow of dry bacteria. The aerosol concentration is derived from microscopic analyses of samples extracted from the bacteria flow. Established calibration methods like Mie scattering at monodisperse spheres and Raman scattering of water are applied to the same set of fluorescence spectra. The achieved cross section data are evaluated with regard to their independency from the measuring system. The results are compared to referenced data. Discrepancies between different datasets in the literature are primarily attributed to different microbiological properties of bacteria due to the respective sample preparation, growth conditions, and aerosolization stress. Elusive optical influences on measurement and calibration as well as inaccuracies of the reference material cause further limitations for the comparability of datasets from different measuring systems.