Narrow-bandwidth red-emitting carbon dots from Epipremnum aureum leaves: “On-Off-On” fluorescent probe for sensitive detection of Hg2+ and Thiram

Accurate and sensitive detection of mercury ions (Hg 2+ ) and thiram is essential for food safety monitoring and environmental protection. Here, an “on-off-on” fluorescent probe based on red-emitting carbon dots (CDs) was fabricated for sequential detection of Hg 2+ and thiram. The CDs exhibited red fluorescence at λ em  = 676 nm with a narrow full width at half maximum of 25 nm. Upon exposure to Hg 2+ , the fluorescence was significantly quenched due to the static quenching mechanism, achieving a limit of detection (LOD) of 25 nM. Notably, upon the addition of thiram, the quenched fluorescence of CDs was recovered due to the strong chelation between thiram and Hg 2+ , thereby enabling sensitive detection of thiram with a LOD of 4.80 nM. The approach was successfully validated using real water samples spiked with Hg 2+ and thiram. The recovery rates were between 97.16 % and 113.83 %, with relative standard deviations below 9.11 %. This study presents a simple, eco-friendly, and effective approach for the sensitive screening of trace contaminants in complex matrices.