Reed-derived fluorescent carbon dots as highly selective probes for detecting Fe³⁺ and excellent cell-imaging agents

A kind of highly selective and sensitive fluorescent probe for detecting Fe³⁺, carbon dots (CDs), was prepared with renewable reed naturally containing C, N, O, and S elements as a green and eco-friendly carbon source by a simple hydrothermal process. The fluorescence of CDs without purification and surface modification can be quenched by Fe³⁺ in a wide concentration range of 0 to 362 μmol L^-1 (concentration of Fe³⁺), with detection limits as low as 0.014 μmol L^-1 in 0-50 μmol L^-1. Characterizations, such as TEM, XPS, Raman and FTIR, confirmed that the static quenching mechanism involved the generation of non-luminescent complexes between Fe³⁺ and functional groups (carboxyl group, sulfur-oxyl group and hydroxyl group) on the surface of CDs and with the aggregation of CDs. More importantly, CDs had good biocompatibility and nontoxicity according to an MTT cell-viability assay, and cells labeled with CDs emitted blue, green and red color fluorescence. Thus, the static quenching mechanism was confirmed. So, this reed-derived natural CD solution can be utilized in detecting Fe³⁺, culture cells, and cell imaging.