Functional preserving carbon dots-based fluorescent probe for mercury (II) ions sensing in herbal medicines via coordination and electron transfer.

Mercury ions (Hg) are one of the compulsory items in the quality control of herbal medicines for its serious toxicity to human health. Highly selective and sensitive Hg detection, especially in complex real samples, is still challenging. In this work, Fluorescent (FL) carbon dots (CDs) with a core-shell structures composed of the crystalline core of stacked sp2-hybridized carbon layers and the shell of functional groups on the periphery of carbon layers are facilely prepared through a one-step hydrothermal synthetic route. They can specifically interact with Hg in aqueous medium to form aggregates, during which coordination of carboxyl functional groups on the surface of CDs with Hg occurred, which facilitated electron transfer from the CDs to Hg. As a result, fluorescence of the CDs was quenched with a high efficiency, making the detection of Hg highly sensitive with the limit of determination (LOD) of 2.2 nM (3σ). With that, detection of Hg in the complex compound herbal medicines samples with highly reproducible results has been successfully realized by using the as-prepared CDs, showing that fluorescent CDs-based probe may have great potential in the quality controls of heavy metals for pharmaceutical analysis.