Ratiometric fluorescent detection of Cu2+ with carbon dots chelated Eu-based metal-organic frameworks

Here, a novel fluorescent carbon dots (CDs)@Eu-2, 6-pyridinedicarboxylic acid (DPA) metal organic frameworks (MOFs) was synthesized by encapsulating CDs into the Eu-DPA MOFs for the detection of Cu 2+ . The as-prepared CDs@Eu-DPA MOFs fluorescent probe was investigated by transmission electron microscopy, Fourier transform-infrared spectroscopy and fluorescence spectroscopy. The results showed the CDs@Eu-DPA MOFs exhibited the uniform ball-flower-like nanostructures and were very stable in aqueous solution due to their nanoscaled size and the ball-flower-like nanostructures. The CDs@Eu-DPA MOFs could emit two kinds of fluorescence which originated from CDs and Eu-DPA MOFs, respectively under a single wavelength excitation at 275   nm. In the presence of Cu 2+ , the fluorescence of Eu-DPA MOFs decreased and the fluorescence of CDs kept constant to result in ratiometric fluorescent response toward Cu 2+ when they were used as the recognition parts and the reference, respectively. The obtained CDs@Eu-DPA MOFs for the detection of Cu 2+ showed a wide linear range (50   nM–10   μM) and a low detection limit (26.3   nM) with high sensitivity, stability and selectivity. The work provides a good method to construct fluorescent sensors based on MOFs.