Luminescent detection of the lipopolysaccharide endotoxin and rapid discrimination of bacterial pathogens using cationic platinum(II) complexes

A luminescence probe based on chloroplatinum(II) complexes of 2,6-bis(benzimidazol-2'-yl) pyridine with hexaethylene glycol methyl ether groups ([Pt(N<^>N<^>N)Cl](+)) was reported for sensing of the lipopolysaccharide (LPS) endotoxin and rapid discrimination of Gram-negative and Gram-positive bacterial pathogens. [Pt(N<^>N<^>N) Cl](+) can be dissolved in aqueous solution with minimal luminescence emission. In the presence of LPS, [Pt(N<^>N<^>N) Cl](+) binds to negatively charged LPS to form LPS-Pt(II) aggregates. The formation of LPS-Pt(II) aggregates enhances the intermolecular Pt/Pt and pi-pi stacking interactions, and consequently leads to luminescence emission centered at 650 nm due to triplet metal-to-metal-to-ligand charge-transfer ((MMLCT)-M-3). The limit of detection (LOD) of LPS is 5.7 nM. We also demonstrate a proof-of-concept application of [Pt(N<^>N<^>N)Cl](+) for rapid and washing-free discrimination of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus within 5 min. The above features of [Pt(N<^>N<^>N)Cl](+) make it a promising sensor for clinical applications in the detection of endotoxins and discrimination of bacterial pathogens.