A robust aminothiazole-based colorimetric sensor for visual detection of Fe³⁺ ions in environmental and pharmaceutical samples

An aminothiazole-based chromogenic chemosensor, (4-methyl-2-(phenylamino)thiazol-5-yl)(phenyl)methanone (MPTP), was synthesized via an iodine-catalyzed one-pot reaction and tailored for the selective and sensitive detection of Fe³⁺ ions. The sensor exhibited a distinct chromogenic transition from pale yellow to brown upon Fe³⁺ binding in ethanol. MPTP demonstrated pronounced positive solvatochromism, Job’s plot analysis confirms a 1:1 binding stoichiometry between MPTP and Fe³⁺, while Benesi-Hildebrand method reveals a high binding constant, indicative of strong complex formation, a low detection limit (LOD = 0.268 µM), and broad pH stability (2–12), with optimal performance in the physiologically relevant range of pH 6–10. The Fe³⁺-induced response was reversible through EDTA-mediated chelation, enabling facile sensor regeneration. A portable paper-based test strip incorporating MPTP reproduced the solution-phase chromogenic response, allowing rapid and visual detection of Fe³⁺ without instrumentation. Environmental and pharmaceutical Fe³⁺ analysis using simulated water and ferric citrate tablets confirmed the sensor’s applicability, achieving a 98% and 102% recovery rate. DFT calculations support the experimental data, attributing the 361 nm band to a π-π* transition with pronounced intramolecular charge transfer, and HOMO-LUMO/MEP analysis highlights nitrogen-rich sites as preferred Fe³⁺ binding centres, further underscoring MPTP as a robust probe for Fe³⁺ detection.