Strategy to synthesize dual-emission carbon dots and their application for pH variation and hydrogen sulfide sensing and bioimaging

In this work, dual emission nitrogen and sulfur co-doped fluorescent carbon dots (DE-CDs) were designed for pH variation and hydrogen sulfide (H2S) sensing and bioimaging through fluorescence enhancement. The DE-CDs with green-orange emission were facilely prepared by one-pot hydrothermal strategy using neutral red and sodium 1,4-dinitrobenzene sulfonate as precursors, manifesting intriguing dual-emission behavior at 502 and 562 nm. As the pH increases from 2.0 to 10.2, the fluorescence of DE-CDs gradually increases. The linear ranges are 2.0-3.0 and 5.4-9.6, respectively, which are attributed to the abundant amino groups on the surface of the DE-CDs. Meanwhile, H2S can be employed as an enhancer to increase the fluorescence of DE-CDs. The linear range is 25-500 μM, and the LOD is calculated to be 9.7 μM. Besides, the DE-CDs can be used as imaging agents for pH variation and H2S sensing in living cells and zebrafish due to their low toxicity and good biocompatibility. All of the results demonstrated that the DE-CDs can monitor pH fluctuations and H2S in aqueous and biological environments, and have promising applications in the fields of fluorescence sensing, disease detection, and bioimaging.