Europium Ion-Based Magnetic-Trapping and Fluorescence-Sensing Method for Detection of Pathogenic Bacteria.

Europium ions (Eu 3+ ) have been utilized as a fluorescence-sensing probe for a variety of analytes, including tetracycline (TC). When Eu 3+ is chelated with TC, its fluorescence can be greatly enhanced. Moreover, Eu 3+ possesses 6 unpaired electrons in its f orbital, which makes it paramagnetic. Being a hard acid, Eu 3+ can chelate with hard bases, such as oxygen-containing functional groups (e.g., phosphates and carboxylates), present on the cell surface of pathogenic bacteria. Due to these properties, in this study, Eu 3+ was explored as a magnetic-trapping and sensing probe against pathogenic bacteria present in complex samples. Eu 3+ was used as a magnetic probe to trap bacteria such as Staphylococcus aureus , Escherichia coli , Enterococcus faecalis , Acinetobacter baumannii , Bacillus cereus , and Pseudomonas aeruginosa . The addition of TC facilitated the easy detection of magnetic Eu 3+ -bacterium conjugates through fluorescence spectroscopy, with a detection limit of approximately ∼10 4 CFU mL -1 . Additionally, matrix-assisted laser desorption/ionization mass spectrometry was employed to differentiate bacteria tapped by our magnetic probes.