Synthesis of fluorescent carbon dots by B/P doping and application for Co²⁺ and methylene blue detection

During the synthesis of carbon dots, different heteroatom doping can change the fluorescence color and the emission wavelength when the same precursor is applied. In this study, we used o-phenylenediamine and L-lysine as raw materials, boric acid or phosphoric acid as different heteroatom dopants, and water as solvent to synthesize doped carbon dots through a simple microwave-assisted method. Finally, two kinds of doped carbon dots with different fluorescence colors under 365 nm UV light were obtained, of which the B-doped carbon dots (B-CDs) showed orange fluorescence, and the P-doped carbon dots (P-CDs) showed red fluorescence. Both carbon dots had satisfactory fluorescence quantum yields and can be used as fluorescence probes. Therefore, we investigated the detection performance of these two carbon dots when they were used as fluorescent probes. B-CDs can selectively detect Co²⁺ with a detection limit of 0.1102 μM, and at the same time, it can realize the naked eye detection of Co²⁺ in a certain concentration range. The P-CDs could sensitively detect methylene blue with a detection limit of 0.048 μM.