<p>A novel long-wavelength fluorescent chemodosimeter based on rhodamine was constructed to monitor Cu²⁺ in the environment and living systems. With the addition of Cu²⁺, this chemodosimeter responded rapidly within 5&#xa0;s and the fluorescence intensity increased about 100 times within 10&#xa0;s. The color of chemodosimeter solution changed from colorless to pink in natural light, while there was an obviously fluorescence changed from colorless to red under a 365&#xa0;nm UV lamp. The fluorescence intensity (588&#xa0;nm) showed a satisfactory linear relationship (<i>R</i>² = 0.9878) with Cu²⁺ concentration (0—10&#xa0;μM) with the detection limit of 7.53&#xa0;nM. Biological imaging experiments of cells and soybean sprouts showed that the chemodosimeter could successfully detect Cu²⁺ in living systems. In addition, the chemodosimeter could be used to monitor Cu²⁺ in real water samples. All in all, this study offers a promising analytical tool for monitoring Cu²⁺ in the environment and living systems.</p> Graphical Abstract <p></p>