Homogeneous Luminescence Detection Based on Lanthanide Coordination Compound

Lanthanide coordination compounds (LnCC), as excellent luminophores, exhibit ultrasensitive responses to the structural details of coordination environments, providing an effective platform for chemical and biomedical detection. Due to the overtones of molecular vibrations in water that cause luminescence quenching, LnCC-based sensors are typically used in heterogeneous systems, where the compounds are dispersed as solid nanoparticles in aqueous solvents. However, this reduces sensor stability, affecting sensitivity and selectivity, and complicates mechanistic analysis. In this work, we developed homogeneous luminescence detection techniques using LnCC and investigated the underlying chemical mechanisms. The Eu-DPA coordination compound was synthesized as a homogeneous detector with good water solubility (140.3 mg/g) and excellent luminescence (92.49% quantum efficiency and >2 ms lifetime at 1 g/L concentration) via multifaceted sonication. Thanks to its homogeneous nature, the sensor achieved high sensitivity, selectivity, and stability for detecting the carcinoid marker 5-hydroxyindoleacetic acid (5-HIAA) in water, plasma, and urine. Eu-DPA exposes numerous pyridine carboxylate oxygen sites that form hydrogen bonds with the amino groups in 5-HIAA. Transient Absorption Spectroscopy (TAS) and Time-Resolved Luminescence Spectroscopy (TRES) further confirm that electrostatic interactions between the hydrogen-bonding sites significantly influence the energy transfer process, as evidenced by changes in luminescence behavior. This work not only addresses the challenge of balancing water solubility and efficient luminescence in lanthanide complexes but also offers new insights into the development of practical biomedical luminescence sensors.