Silane-modified layered double hydroxides with europium sensor for aqueous singlet oxygen detection

Abstract

A silane-modified layered double hydroxide (LDH) hybrid with a covalently coupled europium complex for aqueous singlet oxygen (¹O₂) detection is presented. A Mg/AL-LDH is modified with two alkoxysilanes simultaneously to increase its covalent linkability (using –SH or –NH₂ groups) and to improve its dispersibility in water (using –N⁺(CH₃)₃ groups). The ¹O₂-responsive europium complex is coupled to the –SH or –NH₂ - modified LDH employing epoxyphenanthroline (5,6-Epoxy-5,6-dihydro- [1,10]phenanthroline, “ephen”), which is acting as an ancillary ligand to the europium via its hetero-aromatic N-atoms on one hand and allows the covalent linkage of its epoxy-group to the modified LDH on the other hand. In this manner, the silane chains keep the europium complex away from the chemically active LDH surface, hence maintaining its structural integrity and photophysical properties. The result is a water-dispersible probe with a remarkable response to ¹O₂. This is signaled by the significant increase in the characteristic Eu³⁺ emission at 613 nm resulting in up to a 27-fold increase in emission intensity on exposure to ¹O₂ having a decay time of 380 μs. The resulting Eu-LDH hybrid is applicable for heterogeneous aqueous ¹O₂ detection; its long decay time, useful in time-gated measurements, in conjunction with the biocompatibility of LDH makes it particularly suitable for biological matrices, where ¹O₂ needs to be monitored.