A ratiometric fluorescence sensor based on Eu3+ doped LDH@CMCh gel for visual detection and effective adsorption of tetracycline antibiotics

Abstract

Herein, a ratiometric fluorescence sensor (Eu³⁺/LDH@CMCh gel) was firstly designed by self-assembling Eu³⁺ doped ZnAl layered double hydroxide (LDH) on carboxymethyl chitosan (CMCh) for simultaneously visual detection and effective adsorption of tetracycline antibiotics (TCs). Blue fluorescence at 420 nm of Zn²⁺-sensitized CMCh was quenched by TCs through the inner filter effect, while the red fluorescence at 617 nm generated by the antenna effect was enhanced obviously. Based on reverse variation of two fluorescence signals, sensitive detection of TCs was achieved with a lower LOD (0.041 μM). Besides, the Eu³⁺/LDH@CMCh gel exhibited outstanding adsorption performance for TCs due to the unique porous sponge-like structure. The maximum adsorption capacity of 564.3 mg g^-1 was obtained, aligning well with both the pseudo-second-order and Freundlich model, indicating the chemical adsorption process. Various characterization means and density functional theory showed that the adsorption mechanisms mainly involved hydrogen bonding, electrostatic interaction, and cation-π interaction. Combined with the smartphone, the Eu³⁺/LDH@CMCh gel was successfully applied to realize the portable visual detection of TCs in food matrixes with satisfactory recoveries (83.6 %-118.6 %). Therefore, this work provides a new strategy for sensitive detection and efficient removal of TCs, revealing considerable practical application potential.

Keywords: Adsorption; Eu(3+)/LDH@CMCh gel; Ratiometric fluorescence sensor; Tetracycline antibiotics.