Polychromatic Carbon Dots Prepared from m‑Phenylenediamine and Urea as Multifunctional Fluorescent Probes

The use of nanomaterials such as carbon dots (CDs) as rapid detection fluorescent nanoprobes is a hot topic in the field of analytical chemistry. In this paper, blue, green, and red CDs with high fluorescence quantum yields (24, 54, and 38%, respectively) were obtained from m-phenylenediamine and urea by hydrothermal synthesis and chromatographic separation. After investigating the structures and properties of the obtained CDs, three distinct and sensitive fluorescent nanoprobes with different functions were successfully constructed. The first nanoprobe derived from blue CDs could be used to detect the pH of a strong acid solution (pH 3.0); a rapid detection kit was designed based on it. The second nanoprobe based on Green CDs with ellagic acid (EA) modification allowed the sensitive determination of Fe³⁺ ions in aqueous solutions. The final probe derived from Red CDs could be used to test for organic acids in liquor. The test results of the commercial liquor were consistent with the standard methods. The detection mechanism of the three fluorescent probes was proposed. Using CDs to construct multifunctional fluorescent nanoprobes is beneficial for the application of CDs to rapid and specific detection and recognition.