A review of the use of laser-induced breakdown spectroscopy for bacterial classification, quantification, and identification

The use of laser-induced breakdown spectroscopy to determine the elemental composition of bacterial cells has been described in the peer-reviewed literature since 2003. Fifteen years on, significant accomplishments have been reported that have served to clarify and underscore the areas of bacteriological investigation that LIBS is well-suited for as well as the challenges that yet remain to be faced. This review will attempt to summarize the state of the field by surveying the available body of knowledge. The early days of these experiments, roughly from 2003 to 2007, in which many of the most fundamental experiments were initially conducted will be described. The more in-depth investigations that followed in the subsequent decade will then be detailed. Many important aspects of performing LIBS on bacterial cells were reported on and are summarized here including: the use of chemometric algorithms for statistical classification of unknown spectra; the influence of the mounting substrate on classification; the effect of the testing gas atmosphere and the choice of bacterial cell growth nutrient medium on the measured LIBS spectrum; the efficacy of a LIBS-based test as a genus-level or strain–level discrimination test; the ability of LIBS to determine the cell titer or concentration of cells in the initial sample; the effects that possible contaminations or interferents within the sample would have on the LIBS spectrum; the influence that environmental stresses the cells may be exposed to during growth and the state of reproductive health of the cells could have on the LIBS spectrum; the use of standoff or remote apparatus to minimize the risk to the operators during bacteriological identification of unknown specimens; and the combination of other optical modalities with LIBS to enhance the sensitivity or specificity of identification. Lastly, tables are provided which summarize both every species of bacteria ever tested with LIBS as well as the major lessons learned by the community through 15 years of careful investigation.