Where I am – Chemical microscopy of Eu(III)

Linking microscopy and spectroscopy based on the correlative application of state of the art spectroscopic, microscopic and biochemical methods and equipment is inevitable in the modern time of f-element biochemistry. The aim of this work was the direct visualization and localization in combination with the chemical identification and characterization of f-elements, here Eu(III), interacting with biostructures.
Herein, we utilized chemical microscopy – a combination of light microscopy and high resolution luminescence spectroscopy [1] – in order to spatially resolve the Eu(III) species distribution in an artificial natural sample. In this proof-of-concept study, a ternary system consisting of Eu(III), calcite and the metal reducing bacterium Shewanella oneidensis MR-1 was employed to confirm the applicability of chemical microscopy for environmental samples. Subsequent luminescence spectroscopic mapping and data deconvolution by the means of non-negative iterative factor analysis (NIFA) [2] resulted in three distinct signal sets: one Raman (pure calcite) and two Eu(III) emission spectra. Luminescence species assigned to Eu(III), on the one hand, that has been complexed with biofilm extracellular DNA (magenta-colored - Figure 1) and, on the other hand, protein bonded Eu(III), depicted in green. These findings emphasize the strength of the described analytical technique and open the field for further studies applying Eu(III) as molecular probe in order to understand complex interaction pathways of lanthanides in the environment. The utilization of Eu(III) as a luminescent probe for chemical microscopy additionally revealed the microscopic distribution of the Eu(III) in roots, root cross sections and individual cells presented by several examples.