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

Mercury ions (Hg2+) are one of the compulsory items in the quality control of herbal medicines for its serious toxicity to human health. Highly selective and sensitive Hg2+ 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 Hg2+ in aqueous medium to form aggregates, during which coordination of carboxyl functional groups on the surface of CDs with Hg2+ occurred, which facilitated electron transfer from the CDs to Hg2+. As a result, fluorescence of the CDs was quenched with a high efficiency, making the detection of Hg2+ highly sensitive with the limit of determination (LOD) of 2.2 nM (3σ). With that, detection of Hg2+ 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.