Nitrogen-doped carbon dots for ultrasensitive detection of Hg2+ in traditional Chinese medicine and bioimaging applications†

A nitrogen-doped carbon dots (N-CDs)-based fluorescent sensor was developed for ultrasensitive and selective detection of mercury ions (Hg²⁺) in complex matrices, such as Panax notoginseng (Burk.) F. H. Chen (Sanqi). The synthesized N-CDs exhibited intense blue fluorescence (quantum yield: 35%) with an ultra-small size of 1.93 ± 0.53 nm. Leveraging dynamic quenching mechanisms, the sensor achieved a linear detection range of 0–50 μM for Hg²⁺ and an exceptionally low limit of detection (LOD) of 0.2825 nM, outperforming existing CD-based sensors. The N-CDs demonstrated remarkable selectivity for Hg²⁺ in the presence of interfering ions and complex herbal components. Hg²⁺ in Sanqi samples was quantified by fluorescence analysis (25.5–26.8 μg kg⁻¹, RSD < 2.0%) and cross-validated via Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (24.8–26.2 μg kg⁻¹, RSD < 1.0%), demonstrating N-CDs’ reliability for precise Hg²⁺ detection. Additionally, the N-CDs exhibited excellent biocompatibility and were successfully applied for cellular imaging in A549 cells, showcasing their dual functionality in environmental monitoring and biomedical diagnostics.