Fluorescence lifetime measurements of disulfonated aluminium phthalocyanine in the presence of microbial cells

Abstract

The fluorescence lifetimes of disulfonated aluminium phthalocyanine (AlPcS₂) in the presence of several different microbial cells are measured using the technique of time correlated single photon counting (TCSPC) employing front-face illumination. The microbes studied are: Escherichia coli, Porphyromonas gingivalis (Gram-negative bacteria), Streptococcus mutans (a Gram-positive bacterium), and the yeast Candida albicans. Complex fluorescence decays are observed when AlPcS₂ is in the presence of these microbes; the fluorescence decay data can be fitted to a distribution of exponential lifetimes indicating that the AlPcS₂ molecules experience a range of micro-environments. The average fluorescence lifetimes of AlPcS₂ in the presence of the microbes studied range from 4.85 to 5.95 ns, indicating differences in the cellular localisation of AlPcS₂ with each of the microbes studied. These novel data are presented alongside a brief summary of existing AlPcS₂ fluorescence lifetime data measured both in solution and in model biological systems.