A quinoline colorimetric ionic liquid probe by electrostatic enhancement for visual detection of Fe³⁺ in food

Excessive or insufficient iron(Ⅲ) will pose burdens of human body, and its content is the key to control the function of iron-fortified food. In this regard, a functionalized quinoline ionic probe, benefiting from the electrostatic attraction, was designed for the colorimetric detection of Fe³⁺ in food. This probe formed a 2: 1 complex with Fe³⁺, altering the UV-vis spectra and solution color. The UV-vis detection limit was 0.2 μM, and visually, the color shifted from light-yellow to dark-green as Fe³⁺ concentrations increased, with a visual detection limit of 3.4 μM, meeting the maximum acceptable level of 5.4 μM. Noteworthy, ionic liquid-based sensing paper was constructed for rapid, semi-quantitative Fe³⁺ detection. Furthermore, the satisfying recovery (97.4-102.9 %) was obtained in real samples, showcasing the probe's efficiency. This work demonstrated the potential of ionic liquids for the fast, sensitive, and visual detection of Fe³⁺, offering a promising direction for metal element sensing platforms.