Ratiometric Detection of Cu2+ Using a Luminol-Tb-GMP Nanoprobe with High Sensitivity and Selectivity

A novel ratiometric fluorescent method for the detection of copper ions (Cu2+) based on the stimulus-responsive dual-ligand lanthanide luminol-Tb-GMP coordination polymer nanoparticle (CPNP) fluorescent probe is reported in this study. The luminol-Tb-GMP CPNPs are composed of Tb3+ as the center metal ions and ligand of GMP together with the cofactor luminol ligands as the bridging ligands. In the presence of Cu2+, the fluorescence of GMP-Tb as the response moiety is dynamically quenched, while the fluorescence of luminol used as the reference remains constant. Hence, ratiometric fluorescent monitoring of Cu2+ can be achieved by measuring the ratio of the fluorescence at the 430 nm (F-430) wavelength of luminol to the 547 nm (F-547) wavelength of Tb3+ in the fluorescent spectra of the luminol-Tb-GMP CPNPs suspension. In this sensing approach, when Cu2+ coordinates with a luminol/GMP unit, the fluorescence of the Tb3+ units located in the vicinity Cu2+ will also be quenched. Thus, the sensing sensitivity is highly improved due to the large number of luminol/GMP units in CPNPs. The obtained Cu2+ detection limit is as low as 4.2 nM (S/N = 3), which is approximately 3 orders of magnitude lower than that for the single ligand GMP-Tb CPNPs (3.5 mu M) without luminol doping. The linear range is from 0.01 to 80 mu M. Because luminol is directly linked to the CPNP molecule, which serves as a strong chelating reagent for Cu2+, the common disturbances of Hg2+ and Ag+ are almost completely eliminated, highly improving the selectivity for practical application with little interference. The present method has been successfully applied in the detection of Cu2+ in river water, ascites, and urine samples, indicating that luminol-Tb-GMP CPNPs can be used to detect Cu2+ in environmental water and complexed biological samples.