Preparation and application of achiral UiO-66-NH2 MOFs for enantioselective fluorescent detection of lysine enantiomers.

ABSTRACT

Lysine (Lys) is an essential nutrient that plays a crucial role in the growth and development of living organisms. Chiral analysis of Lys holds significant importance for ensuring the safety of food, pharmaceuticals, and health products. In this work, an achiral Zr-based metal organic frameworks (MOFs), UiO-66-NH2, was proposed as a fluorescent probe to achieve rapid response to l-lysine (L-Lys) in solution. Additionally, Zr4+ in the skeleton of UiO-66-NH2 framework exhibited different binding capacities towards Lys enantiomers, leading to distinct fluorescence responses for L-Lys and d-lysine (D-Lys). Leveraging these properties, the UiO-66-NH2 probe enabled accurate determination of L-Lys concentrations in solution, as well as the enantiomeric excess (ee) values of Lys solutions. Notably, in the detection of Lys enantiomers, the achiral UiO-66-NH2 acted as both a chiral selector and a fluorescent indicator, greatly improving the efficiency and stability of the detection system. The probable mechanism was further elucidated by pH titration experiments and density functional theory calculations. Additionally, the general applicability of this mechanism was validated by similar amino MOFs. The application of the UiO-66-NH2 fluorescent probe in analysis of infant formula milk powders and liquid milk samples confirmed the reliability of the method. Moreover, the construction of fluorescence test paper by immobilizing UiO-66-NH2 onto filler papers enabled the rapid identification of Lys enantiomers. Compared to previous fluorescent analyses of chiral amino acids assisted by additional metal ions, this study presented a novel approach and methodology that offers high efficiency, stability, reproducibility and reusability for the identification and detection of Lys enantiomers, highlighting the potential of the UiO-66-NH2 fluorescent probe in advancing analytical techniques.