Fluorescence-based detection of ammonium ferric citrate using Zn(II)-Based coordination polymer: A study on selectivity, mechanism, and environmental application

Fluorescence-based sensing has emerged as a powerful tool for detecting trace biomolecules in various analytical applications. In this study, a Zn(II)-based coordination polymer (CP), [Zn(NBA)(HDPP)]_n (1) (DPP = 2,5-di-4-pyridinylphenol, H₃NBA = 5-nitro-1,2,3-benzenetricarboxylic acid), was synthesized and explored as a selective and sensitive fluorescence sensor for the detection of ammonium ferric citrate (AF). Selectivity studies revealed that CP 1 demonstrated negligible fluorescence quenching in the presence of other biomolecules such as urea, tryptophan, and uric acid, establishing its specificity for AF. Mechanistic investigations, including Inner Filter Effect (IFE) correction and X-ray Photoelectron Spectroscopy (XPS), revealed that the fluorescence quenching was primarily attributed to the IFE effect and Fe³⁺ coordination interactions with nitrogen and oxygen donors in CP 1. The quenching constant (K_sv) was determined to be 1.12 × 10³ M⁻¹, with a detection limit of 1.94 × 10⁻⁴ M, indicating a high sensitivity. The fluorescence lifetime of CP 1 increased from 6.54 μs to 7.47 μs upon interaction with AF, suggesting changes in the excited-state molecular environment. The practical applicability of this sensing approach was evaluated in real water samples, including deionized (DI) water, tap water, and river water, with recovery rates ranging from 95.03 % to 115.08 %, demonstrating the accuracy and reliability of the method. This study establishes CP 1 as an effective, selective, and sensitive fluorescent sensor for AF detection, with potential applications in environmental monitoring and bioanalytical fields.