The nucleotides play multiple fundamental roles that are essential in biochemical enzymatic reactions and signaling pathways. Many diseases are closely associated with their dysregulation. Therefore, reliable and sensitive optical probes to discriminate various nucleotides are essential in biochemistry, drug discovery, and disease diagnosis. Furthermore, developing reliable, easy-to-use optical sensors for extremely toxic organophosphonates/nerve-agents is critical to counter public health threats. Luminescent lanthanide(III) complexes have emerged as promising optical bioprobes owing to intraconfigurational f → f transitions. Herein, we present strategically designed Eu(III) probes: [Eu(THC)(X)3]Cl (Eu.1) and [Eu(TBC)(X)3]Cl/Br (Eu.2) containing pentadentate terpyridine dicarboxylates: 4'-(3,4,5-trihydroxyphenyl)-[2,2':6',2″-terpyridine]-6,6″-dicarboxylic acid (THC) and 4'-phenyl-[2,2':6',2″-terpyridine]-6,6″-dicarboxylic acid (TBC) and X = solvent. The Eu.1 probe is systematically evaluated for discrimination of various NPs and as a luminescent chemodosimetric probe for diethyl chlorophosphate (DCP) as a G-series nerve agent mimic. The time-delayed luminescence is used for discrimination between various adenine-based NPs under physiological conditions. The Eu.1 probe shows high affinity and selectivity for ADP enabling continuous monitoring of the ADP/ATP ratio in a simulated enzymatic reaction. Additionally, Eu.1 acted as a chemodosimetric probe for DCP. The interaction produces a change in the sensitization pathway, enhancing the Eu(III)-based luminescence with a ppb level of detection of DCP (LOD = 758 ppb). Our innovative approach expands applications of lanthanide luminescence for probing nucleotides and the detection of lethal nerve agents.