Color-multiplexing europium doped carbon dots for highly selective and dosage-sensitive cascade visualization of tetracycline and Al3+

Herein, we report a dosage-sensitive europium doped carbon dots (Eu-CDs) with a wide and consecutive color variation from blue to red and reversely from red to blue response to the cascade presence of tetracycline (TC) and aluminum ions (Al3+). With the dosage variation of TC, the fluorescence color of Eu-CDs gradually changes from blue to light purple to final red. The fluorescence intensity ratio of I620/I468 exhibits a linear relationship in the range of 0–100 μM with a detection limit (LOD) of 6.9 nM. The cascade addition of different concentration of Al3+ could reversely change the fluorescence color from red to pink to final blue. A good linear relationship of I468/I620 in the concentration range of 0–50 μM with a LOD of 28.6 nM was obtained. The smartphone-assisted point-of-care testing platform was constructed and displayed dosage scale as low as 13.2 nM and 160 nM for TC and Al3+, respectively. This strategy was further successfully used for on-site visual detection of TC and Al3+ in real samples with satisfied recovery ranged from 93.30% to 108.88%. The strategy proposes a bright future of fluorescent colorimetric sensors for the extensive applications in the assays of environments, medicines, and foods.