Ratiometric fluorescence analysis provides the feasibility for visual quantitative sensing by presenting continuous color changes. Herein, dual-emission carbon dots (D-CDs) have been developed for ratiometric recognition of Co²⁺ and EDTA, along with successive fluorescence variation of yellow, purplish-pink, purple, light blue, and dark blue. D-CDs have been synthesized by microwave-assisted heating of tetracycline and manifest dual emissions at 562 nm and 610 nm under 450 nm excitation. Intriguingly, the emissions at 562 nm and 610 nm are quenched while a ratio rising emission emerges at 482 nm upon introducing Co²⁺, which displays ratiometric fluorescence emission characteristics (I₄₈₂/I₅₆₂) in the range of 0.25–400 µM with significant fluorescence varying from yellow, purplish-pink, purple, light blue, to dark blue. Subsequent addition of EDTA could ratiometric recover the fluorescence of D-CDs in the range of 50–130 µM with the fluorescence returning from dark blue, light blue, purple, purplish-pink, to yellow. More crucially, integrating continuous color changes and color recognizer APP in the smartphone, visual quantification of Co²⁺ and EDTA can be realized based on the ratio of blue value and red value (B/R) with linear ranges of 0–400 µM and 0–300 µM, respectively. Furthermore, proposed D-CDs could be extended as a visual biosensing platform for tracking Co²⁺ and EDTA in living cells, which have potential application prospect in biosystem.

比率荧光分析通过呈现连续的颜色变化为视觉定量传感提供了可行性。在此，开发了双发射碳点 (D-CD) 用于 Co ²⁺和 EDTA 的比例识别，以及黄色、紫粉红色、紫色、浅蓝色和深蓝色的连续荧光变化。D-CD 已通过四环素的微波辅助加热合成，并在 450 nm 激发下在 562 nm 和 610 nm 出现双发射。^{有趣的是，在引入 Co 2+}后，562 nm 和 610 nm 的发射被淬灭，而在 482 nm 出现比率上升的发射，其显示比率荧光发射特性 (I ₄₈₂ /I ₅₆₂) 在 0.25–400 µM 的范围内，具有从黄色、紫粉色、紫色、浅蓝色到深蓝色的显着荧光。随后添加 EDTA 可以比例恢复 50-130 µM 范围内的 D-CD 荧光，荧光从深蓝色、浅蓝色、紫色、紫粉色到黄色返回。更关键的是，在智能手机中集成连续变色和颜色识别APP，可以根据蓝值和红值的比值（B/R）实现Co ²⁺和EDTA的可视化定量，线性范围为0-400 µM，分别为 0–300 µM。^{此外，所提出的 D-CD 可以扩展为跟踪活细胞中 Co 2+}和 EDTA的视觉生物传感平台， 在生物系统中具有潜在的应用前景。