Chinese food seasoning derived carbon dots for highly selective detection of Fe3+ and smartphone-based dual-color fluorescence ratiometric visualization sensing

Carbon dots were obtained from Tangshai, a Chinese food seasoning, using a simple and green method through dialysis. Tangshai-derived carbon dots (TSCD) exhibited unique fluorescent emission properties that can be selectively suppressed by Fe3+ over other heavy metal ions including Fe2+. Based on the Benesi-Hildebrand equations study, a ten times larger coordination constant of Fe3+-TSCD than that of Fe2+-TSCD was obtained, which proved the highly selective superiority. Therefore, a fluorescence quenching method for sensitive detection of Fe3+ was established with two linear ranges of 1–80 μmol L−1 and 200–500 μmol L−1 and the limit of detection (LOD) was 0.41 μmol L−1 (3σ). The real sample detection was performed with satisfactory and validated results. Besides, coupled with orange emissive carbon dots (OCD) whose fluorescence can be enhanced by Fe3+, a dual-color fluorescence ratiometric sensor for Fe3+ was established from the opposite fluorescence responses, and visualization sensing was actuated by a smartphone. This work facilely extracted CDs from Chinese food seasoning and revealed the mechanism of selective sensing for Fe3+, facilitating the green synthesis of CDs and heavy metal ions sensing.