MRI and fluorescence studies of Saccharomyces cerevisiae loaded with a bimodal Fe(III) T₁ contrast agent

Labeling of cells with paramagnetic metal complexes produces changes in MRI properties that have applications in cell tracking and identification. Here we show that fungi, specifically the budding yeast Saccharomyces cerevisiae, can be loaded with Fe(III) T₁ contrast agents. Two Fe(III) macrocyclic complexes based on 1,4,7-triazacyclononane, with two pendant alcohol groups are prepared and studied as T₁ relaxation MRI probes. To better visualize uptake and localization in the yeast cells, Fe(III) complexes have a fluorescent tag, consisting of either carbostyril or fluoromethyl coumarin. The Fe(III) complexes are robust towards dissociation and produce moderate T₁ effects, despite lacking inner-sphere water ligands. Fluorescence microscopy and MRI T₁ relaxation studies provide evidence of uptake of an Fe(III) complex into Saccharomyces cerevisiae upon electroporation.