A novel near-infrared-emitting selenolactone-cyanine chemosensor platform for ultra-trace mercury (II) detection in environmental, food and living cell samples

A novel near-infrared (NIR) fluorescent and colorimetric probe, NIR-2 , was designed and synthesized for the highly selective and sensitive quantification of Hg²⁺ ions in real samples. The interaction between NIR-2 and Hg²⁺ triggered a structural transformation from ring-closed fluorescence turn-off selenolactone structure to ring-open acid form, leading to a visible color shift and notable fluorescence enhancement. Spectroscopic techniques, including HRMS, FT-IR, and NMR, confirmed the molecular structure and interaction mechanism between the probe and Hg²⁺ ions. NIR-2 demonstrated outstanding sensing performance for Hg²⁺ ions across a wide concentration range, with detection limits as low as 3.77 × 10⁻¹⁰ M for UV-Vis and 4.54 × 10⁻⁹ M for fluorescence, and a rapid response time of 10 s. The probe was successfully validated with real-world applications, including water and food sample analysis, achieving high recovery rates. Additionally, the development of a smartphone-based detection method enables rapid, on-site, and cost-effective mercury monitoring. To the best of our knowledge, the range of 1.66 × 10⁻⁹ M to 7.50 × 10⁻⁶ M that we achieved with the smartphone-based Hg²⁺ detection is the most sensitive reported in the literature. Moreover, cell toxicity assessments and imaging studies confirm that NIR-2 functions effectively in biological environments for Hg²⁺ detection. Overall, these findings highlight the practical utility of NIR-2 as a promising tool for environmental, food, and health safety applications.