AIE-active cyclometalated iridium(iii) complexes for the detection of lipopolysaccharides and wash-free imaging of bacteria

Infectious diseases caused by bacteria pose a major threat to human health and are currently one of the leading causes of mortality worldwide. Therefore, the development of probes for rapid detection of bacteria and their pathogenic components is highly essential. Aggregation-induced emission (AIE)-active compounds have shown great promise for the diagnosis of bacterial infections. In this study, we have synthesized three cationic AIE-active cyclometalated iridium(III) polypyridyl complexes viz., [Ir(C^N)2(N^N)]Cl2 (Ir1-Ir3), where C^N is a cyclometalating ligand such as pq = 2-phenylquinoline (in Ir1), pbt = 2-phenylbenzothiazole (in Ir2), and dfppy = 2-(2,4-difluorophenyl)pyridine (in Ir3), and N^N is a 2,2'-bipyridine derivative, for detection of lipopolysaccharide (LPS) in aqueous solution and wash-free imaging of bacteria. These complexes exhibit rapid sensing of LPS also known as endotoxin released by the bacteria, with a detection limit in the nanomolar range being determined by fluorescence spectroscopy within 5 min. Detection of both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria by the complexes is visible to the naked eye and was also observed by fluorescence microscopy imaging. The above features of the complexes make them a promising scaffold for the detection of bacterial contamination in aqueous samples.