A turn on fluorescent sensor based on lanthanide coordination polymer nanoparticles for the detection of mercury(II) in biological fluids

Coordination polymers have recently emerged as very fascinating materials due to their tunable nature. In this work, we develop a lanthanide coordination polymer (CPNP)-based turn on sensor for Hg²⁺ detection by employing the strategy of inner filter effect (IFE). This kind of CPNP is composed of europium ions (Eu³⁺) as metal centers and isophthalic acid (IPA) as bridging ligands that can sensitize the fluorescence of Eu³⁺. Because the excitation spectrum of Eu/IPA CPNPs greatly overlaps with the absorbance band of imidazole-4,5-dicarboxylic acid (Im), the presence of Im can significantly quench the fluorescence of Eu/IPA CPNPs through a process of IFE. Upon the addition of Hg²⁺, however, the Im-quenched fluorescence of Eu/IPA CPNPs can be recovered due to the suppression of the IFE of Im through the formation of a Hg/Im complex. As a fluorescent sensor for Hg²⁺ detection, Eu/IPA CPNPs not only show high sensitivity up to a detection limit of 2 nM and excellent selectivity, but also possess the advantages of fast response, simple preparation procedure and flexible sensing performance. More importantly, interference from the background fluorescence of biological fluids can be efficiently eliminated via a time-resolved detection mode. The presence of the sensing strategy would be beneficial to the design of other lanthanide coordination polymer-based fluorescent sensors.