Lanthanide ions sensitizing ligands

Another concern is that, for a 9-coordinate lanthanide ion in aqueous solution bound to a single tridentate DPA ligand, the six coordinated water molecules will strongly quench the luminescence (92). To eliminate the potential for solvent quenching and improve the sensitivity of the assay, we explored the use of a hexadentate ancillary ligand to encapsulate the Tb ion and exclude solvent from the coordination sphere without impeding dipicolinate chelation. 

Ancillary ligands can dramatically improve detection strategies based on sensitized Ln luminescence by stabilizing the lanthanide to pH variations. Such enhancements in stability and reproducibility allow the use of lanthanide sensors in situ and also potentially in vivo, where free lanthanide ions might precipitate and/or have toxic effects. 

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