Single-cell inductively coupled plasma mass spectrometry (scICP-MS) has emerged as a powerful tool to evaluate the elemental composition at a single-cell level. While this technique has been successfully applied to the analysis of several microorganisms (e.g., bacteria, yeasts) and human cells, it has not yet been applied to the analysis of extremophiles, particularly halophilic ones. The lack of studies on this regard is not surprising considering the complexity of halophilic cell culture media (80-150 g L^-1 total dissolved solids) that gives rise to severe spectral and non-spectral interferences.

This study aimed to develop a robust methodology for characterizing the halophilic archaeon Haloferax Medierranei when this microorganism is exposed to Pb, Se and Te using scICP-MS analysis. To this end, different sample introduction systems and dilutions strategies were tested with the aim to maximize detection capabilities and minimize potential cell lysis. Our results indicated that combining a Meinhard nebulizer with a Scott spray chamber and high matrix introduction (HMI) system, along with an on-line dilution system, achieved the best results by effectively reducing the impact of high salt concentrations on the analysis. This strategy was successfully employed to characterize H. mediterranei exposed to Pb, Se and Te. We observed that Pb was internalized by the cells while exposure to Se and Te resulted in the formation of Se and Te nanoparticles, respectively.