<p>Herein, a colorimetric and smartphone dual-channel sensor has been constructed for the sensitive detection of acetone based on a chemically driven redox-cycling reactive system. In the redox-cycling system, <i>o</i>-phenylenediamine (OPD) acted as the colorimetric substrate. Initially, colorless OPD was oxidized by Cu²⁺ ions to generate Cu⁺ ions and light yellow 2,3-diaminophenazine (DAP). The Fenton-like reaction between hydrogen peroxide (H₂O₂) and generated Cu⁺ ions initiated the production of Cu²⁺ ions and hydroxyl radicals (·OH). The resulting ·OH and reproduced Cu²⁺ ions could further catalyze other OPD molecules, leading to the formation of more light yellow DAP molecules, with a distinct ultraviolet absorption peak appearing at 440&#xa0;nm. And this process continued until all OPD was completely consumed in the cycling reaction system. Interestingly, acetone was introduced into the redox-cycling system, leading to a colorless solution and a reduction of absorbance intensity at 440&#xa0;nm. Based on this phenomenon, a colorimetric sensor with excellent sensitivity and selectivity has been designed for the visual detection of acetone. The sensor exhibited a linear correlation with acetone concentrations within the range of 2&#xa0;μM to 5&#xa0;mM, achieving a detection limit of 0.5&#xa0;μM. Notably, RGB color space analysis was performed for the quantitative detection of acetone with the assistance of a smartphone. The results were in good agreement with the data obtained via UV-visible absorption spectroscopy. Furthermore, the strategy realized the&#xa0;rapid detection of acetone in real tap water, river water, and lake water samples.</p> Graphical abstract <p></p>