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In this study, a pH-sensitive indicator solution for the colorimetric naked-eye detection of dissolved carbon dioxide at room temperature was developed with the aim of environmental monitoring. The indicator solution was produced by the polyvinyl alcohol-coated green synthesized iron oxide nanoparticles and the natural anthocyanin extracted from red cabbage. The pH change upon carbon dioxide dissociation occurred in the indicator solution. The reaction was investigated using the stopped-flow method by monitoring the pH measurements at different dissolved CO2 concentrations. The indicator solution changed color from blue to pink within a few seconds with pH change on the acidic side and returned to its initial state spontaneously without any treatment at the end of the CO2 gas. The indicator solution showed sensitivity to dissolved CO2 concentrations in the range of 600 − 3200 ppm in a fast reaction time and complete reversibility. [ABSTRACT FROM AUTHOR]