Composite Eu@Cd-CP as a fluorescent probe for the detection of some food additives

A transition metal coordination polymer (CP), [Cd(Hdpcp)]_n (Cd-CP) was prepared based on 3-(2,4-dicarboxyphenyl)-6-carboxypyridine ligand (H₃dpcp), and then its composite Eu@Cd-CP was synthesized by the post-modification through loading Eu³⁺ ions on Cd-CP. Eu@Cd-CP has outstanding fluorescence stability in aqueous solution with a wide range of pH. Furthermore, Eu@Cd-CP can distinguish sodium salicylate (SS) and sodium dehydroacetate (SA) in some food additives by quenching the characteristic fluorescence of Eu³⁺ ion. Eu@Cd-CP is the first known CP-based fluorescent probe for selective detection of SS and SA. In addition, the fluorescence mechanisms of discerning above analytes by Eu@Cd-CP have been thoroughly evaluated. It has found that synergistic effect of the dynamic process, photoinduced electron transfer (PET) process, energy absorption competition, and formation of Eu-O bonding interactions in sensing SA lead to the fluorescence quenching of Eu@Cd-CP. The fluorescence response mechanism of Eu@Cd-CP with SA is ascribed to the combination of the dynamic process, PET process, and energy absorption competition. A series of portable devices based on Eu@Cd-CP including fluorescence test strips, lamp beads, and composite films were developed to discern SS and SA via visual changes in luminescence color. This composite material can be potentially used as a multifunctional fluorescent probe for practical applications.