Lanthanide ternary complex as a fluorescent probe for highly sensitive and selective detection of copper ions based on selective recognition and photoinduced electron transfer

Copper ions have a very important role in human health, industrial and agricultural production. Herein, lanthanide ternary complex of 2,6-pyridinedicarboxylic acid (DPA)-Eu3+-polyethyleneimine (PEI) as a fluorescent probe was thus fabricated for highly sensitive and selective detection of copper ions. PEI itself is non-fluorescent, the PEI-Eu3+complex is also non-fluorescent, and PEI has specific recognition to copper ions due to its higher affinity ability to copper ion than other metal ions. It was found that Cu2+ ions cannot quench the characteristic fluorescence of Eu3+ in the DPA-Eu3+ system, while in the DPA-Eu3+-PEI system, Cu2+ ions can greatly quench the characteristic fluorescence of Eu3+ due to photoinduced electron transfer (PET). The luminescent and quenching mechanism was also discussed in detail. The DPA-Eu3+-PEI probe not only has high sensitivity and selectivity, but also has very rapid fluorescence response and the response time is only 1 min. A good linear relationship between the fluorescence ratios of F0/F and the concentrations of Cu2+ was obtained in the range of 0.02∼10.0 μM (R2 = 0.998), and the limit of detection (LOD) is 8.0 nM. The probe was successfully applied for the detection of Cu2+ ions in the lake and river water samples, wastewater and urine samples. This work may provide a new strategy for fabricating simple and effective fluorescence probe and a promising application for the rapid and on-site detection in environmental monitoring and biological fluids.