Bacterial spores, or endospores, are produced by certain genera of bacteria under stress and are considered to be one of the most resilient forms of life on Earth.  Detection of endospores is vital for industries ranging from planetary protection to homeland security.  We are investigating an improvement of the current bacterial spore detection assay based on Tb-DPA luminescence through the implementation of a DPA-specific Tb³⁺ receptor site.  The use of a receptor site ligand such as DO2A (1,4,7,10-tetraazacyclododecane-1,7-diacetate) can increase both the sensitivity and selectivity of the assay.  The ternary complex [Tb(DO2A)(DPA)]^- has been characterized via crystallographic and spectroscopic methods.  The DO2A-DPA binding interactions are being investigated through the luminescent lanthanide series, consisting of dysprosium, terbium, europium and samarium, with ionic radii varying from 1.08 to 1.13 Å.