Lignin-derived carbon dots as a fluorescence and smartphone auxiliary sensing platform for the detection of Co(II) and VB12

Lignin-derived carbon dots (L-CDs) were synthesized via a simple one-step hydrothermal method using sodium lignosulfonate and polyethylene polyamine as carbon and nitrogen sources, respectively. The obtained L-CDs exhibited strong blue fluorescence, which was effectively quenched by Co(II) and VB 12 through an inner filter effect (IFE), accompanied by distinct color changes under both visible and ultraviolet light. Taking advantage of this property, a smartphone-assisted visual sensing strategy was developed for the rapid and portable detection of Co(II) and VB 12 with high selectivity and sensitivity. The detection limits were as low as 0.17 μM for Co(II) and 0.03 μM for VB 12 . Furthermore, the proposed sensing platform was successfully applied to the determination of Co(II) in environmental water samples and VB 12 in pharmaceutical formulations. This work not only demonstrates a novel design of carbon dot-based dual-mode sensors but also highlights the value-added utilization of lignin in analytical applications.