Orange-emissive N,S-co-doped carbon dots for label-free and sensitive fluorescence assay of vitamin B12

Nitrogen and sulfur co-doped carbon dots (N,S-CDs) with strong orange fluorescence were fabricated through a facile hydrothermal method using o-phenylenediamine and thiourea as precursors. The N,S-CDs exhibited excitation-independent photoluminescent behavior with excellent stability. The largest emission peak at 565 nm occurred at an excitation wavelength of 420 nm, and the quantum yield (QY) was 14.3%. It was found that the absorption spectra of vitamin B12 (VB12) overlaps with the emission peak of the N,S-CDs to a large extent, and based on the inner filter effect (IFE) between VB12 and N,S-CDs, a label-free and sensitive detection method of VB12 in drugs was established. Under optimal conditions, the concentration of VB12 exhibited a satisfactory linear correlation with the fluorescence quenching degree ΔF/F0 of the reaction system at 565 nm in the range of 0.25–20 μM, and the detection limit was 77.5 nM. The N,S-CDs with orange fluorescence emission show huge potential for use in the field of biological analysis.