Hybrid polyurethane–MOF platform for turn-on fluorescent sensing of Cu2+ ion

Abstract

The pervasive contamination of water resources by heavy metal ions poses serious threats to environmental safety and human health, creating an urgent demand for simple, sensitive, and selective sensing platforms. Herein, a robust polyurethane foam (PUF)-supported UiO-66-NH₂–calcein composite is developed as a solid-state fluorescent sensor for the selective detection of Cu²⁺ ions in aqueous media. The immobilization of calcein within the porous UiO-66-NH₂ framework and its subsequent integration into a PUF matrix provides a stable, highly accessible, and reusable fluorescence platform. Structural and spectroscopic characterization confirms the successful formation and homogeneous distribution of the composite components. Fluorescence screening against a series of metal ions demonstrates that, although several ions can interact with the sensor, a markedly enhanced and selective fluorescence response toward Cu²⁺ is achieved under mildly acidic conditions (pH 5). The sensor exhibits a linear fluorescence response toward Cu²⁺ over the micromolar concentration range with a low detection limit of 0.011 µM. The composite also exhibits mechanical integrity and operational reusability, with no significant signal loss. The foam-based architecture enables rapid mass transfer, improved light penetration, and convenient handling, making the platform well-suited for portable and on-site water analysis. This work presents an effective strategy for constructing MOF–polymer fluorescent composites for selective Cu²⁺ sensing and practical environmental monitoring. The PUF/UIO-66-NH–calcein nanocomposite exhibits remarkable fluorescence sensitivity toward multiple metal ions at pH 7, achieving ultra-low limits of detection of 0.0013 µM for As³⁺, 0.0049 µM for Cd²⁺, 0.009 µM for Zn²⁺, 0.0049 µM for Cu²⁺, and 0.0081 µM for Ca²⁺, while maintaining stable performance under aqueous conditions.