Fluorescence on and off sensing platform based on europium nanosheets for the detection of DPA and Cu²⁺ ions

With the development of society, the modern environment has put forward higher requirements for analysis and detection. This work proposes a new strategy for the construction of fluorescent sensors based on rare-earth nanosheets. Organic/inorganic composites were obtained by the intercalation of 4,4'-stilbene dicarboxylic acid (SDC) into layered europium hydroxide, and then the composites were exfoliated to form nanosheets. Taking advantage of the fluorescence emission characteristics of SDC and Eu³⁺, a ratiometric fluorescent nanoprobe was constructed, which realized the detection of dipicolinic acid (DPA) and Cu²⁺ in the same system. With the addition of DPA, the blue emission of SDC gradually decreased and the red emission of Eu³⁺ gradually increased, when Cu²⁺ was added, the emission of SDC and Eu³⁺ were gradually weakened. The experimental results showed that the ratio of fluorescence emission intensity (I₆₁₉/I₃₉₄) of the probe had a positive linear relationship with the concentration of DPA, and a negative linear relationship with the concentration of Cu²⁺, thus realizing the high sensitivity detection of DPA and a wide detection range of Cu²⁺. In addition, this sensor also exhibits potential visual detection possibilities. This is a multifunctional fluorescent probe that provides a novel and efficient method for the detection of DPA and Cu²⁺, which broadens the application field of rare-earth nanosheets.