One method to enhance the sensitivity and selectivity of our microbial event monitor involves the construction of a supramolecular receptor site specific for DPA. To this end, we are exploring several macrocyclic ligands that bind well to the Tb3+ ion and selectively bind DPA over potential interferents. The ideal ligand could then serve as both a DPA-receptor site and a synthon on which functional groups could be appended to anchor the sensing complex to a solid substrate, such as a fiber optic surface. We are currently characterizing several of these ternary complexes for future modification and later use as sensors.

One ligand in particular has shown promise for use in endospore detection assays. DO2A (1,4,7,10-tetraazacyclododecane-1,7-bisacetic acid) exhibits binding of Tb3+ that is near unity at nanomolar concentrations and improves the lanthanide's affinity for DPA by almost two orders of magnitude. The [Tb(DO2A)]+ binary complex is more stable over a much broader pH range than the Tb3+ ion alone, which tends to form hydroxides and precipitate out of solution in basic conditions; further, the complex successfully mitigates ionic interferents, such as that of phosphate and carbonate.  Binding studies and theoretical modeling are currently underway in our labs to ascertain the mechanism behind this enhanced binding affinity and improved stability.  Modifications to the DO2A ligand are also being pursued to optimize DPA binding and improve the versatility of this binary complex as a sensor of bacterial spores.

publications

Detection of bacterial spores with lanthanide-macrocycle binary complexes.  Cable, M.L.; Kirby, J.P.; Levine, D.J.; Manary, M.J.; Gray, H.B.; Ponce, A.  Journal of the American Chemical Society, 2009, 131(27), 9562-9570. [PDF]

Principles for engineering molecular receptor sites.  Contakes, S.M.; Cable, M.L.; Kirby, J.P.; Ponce, A.  In Bottom-up Nanofabrication: Supramolecules, Self-Assemblies, and Organized Films, Eds. Ariga, K.; Nalwa, H.S., American Scientific Publishers, 2009.

Spectroscopic analysis of ligand binding to lanthanide-macrocycle platforms.  Kirby, J.P.; Cable, M.L.; Levine, D.J.; Gray, H.B.; Ponce, A.  Analytical Chemistry, 2008, 80(15), 5750-5754. [PDF]

Bacterial spore detection by [Tb3+(macrocycle)(dipicolinate)] luminescence.  Cable, M.L.; Kirby, J.P.; Sorasaenee, K.; Gray, H.B.; Ponce, A.  Journal of the American Chemical Society, 2007, 129, 1474-1475. [PDF]