<p>Development of a supramolecular fluorescent sensor for thiamethoxam (TMX) detection led to the synthesis of an imidazole-functionalized 2,6-dihydroxyacetophenone[4]arene (2,6IMD). Upon binding to TMX, 2,6IMD exhibited a pronounced fluorescence enhancement, accompanied by the emergence of a far-red emission band and a distinct colour change from yellow to pink, enabling both spectroscopic and visual detection. A linear response was obtained over the concentration range of 5-120 nM, with a detection limit of 1.22 nM and a binding constant of 3.75 × 10⁷ M^− 1. The recognition mechanism was elucidated through Job’s plot analysis, ¹H NMR titration, and DFT calculations, confirming strong host-guest interactions. High selectivity was observed against structurally related pesticides and potential interfering species. The analytical applicability of the method was demonstrated in fruit, water, soil, and agricultural runoff samples, affording recoveries of 95.33% to 103.80% with low relative standard deviations, and the results showed good agreement with LC-MS/MS validation. Furthermore, integration with paper-strip and smartphone-assisted RGB analysis enabled rapid on-site monitoring. These findings demonstrate the potential of 2,6IMD as a portable and sensitive platform for TMX determination in environmental and food matrices.</p> Graphical Abstract <p></p>