On the bases of “seeing is believing” concept and the existing theory of coordination chemistry, we innovatively designed and synthesized a visual-volumetric sensor platform with fluorescein and uracil functionalized polyacrylamide hydrogel for the first time. Without the aid of complicated instruments and any power sources, the sensor enables quantitative detection M level by reading graduation on a pipette with the naked-eye. The sensor undergoes volumetric response and shows a wide linear response range to (~) with of the detection limit. The high selective (easily distinguished from other common metal ions), rapid response (~30min) and acceptable reproducibility (RSD<5% in all cases) demonstrated that the developed sensor is suitable for practical use onsite for the determination of while conveniently being low cost, simple and portable. The design principles of the obtained materials and the construction techniques and methods of the sensors in our work provide a new idea for the research and development of smart materials and series of visual-volumetric sensors for other analytes.