Smartphone-assisted detection of mercury ion using Al-doped carbon dots for environmental water monitoring

The monitoring of heavy metal ions, especially mercury (Hg²⁺), has become increasingly important due to their high toxicity, environmental persistence, and severe risks to human health. Herein, aluminum-doped carbon dots (Al-CDs) were synthesized via a one-step hydrothermal process using glutathione and AlCl₃·6H₂O as precursors. The resulting Al-CDs emitted strong and stable fluorescence, achieving a high quantum yield of 55.17%. The fluorescence of Al-CDs was efficiently and selectively quenched by Hg²⁺, enabling highly sensitive detection with a low limit of detection of 0.018 μM. This sensing method displayed remarkable selectivity toward Hg²⁺ over other ions and biomolecules. For application in real water samples, this method delivered successful outcomes with high recovery rates. To support on-site detection, a smartphone-based sensing system and portable fluorescent test strips were developed, offering a convenient, low-cost, and user-friendly approach for mercury monitoring. This study demonstrates great potential of Al-CDs as efficient fluorescent probes for environmental analysis and offers a practical strategy for the facile and visual detection of toxic heavy metal ions.