Architecture of a novel NIR and switch-on fluorescent chemosensor based on mercapto propanehydrazide-functionalized chromenylium-cyanine for the quantification of mercury(II) in environment and living cells

A novel probe NIR8 decorated with colorimetric, fluorometric, turn-on, and NIR properties was designed and synthesized using the chromenylium-cyanine platform for sensitive and selective quantification of Hg²⁺ in real samples. The interaction between the probe and Hg²⁺ resulted in the opening of the closed spirolactam ring of the chromenylium-cyanine platform, leading to a notable color shift from yellow to green. Concurrently, ratiometric spectral changes at 380 and 725 nm for UV–Vis and signal enhancement at 755 nm for fluorescence were observed. HRMS, FT-IR, and DFT calculations clarified the interaction between NIR8 and Hg²⁺, and Job's method confirmed the 1:1 coordination ratio between them. The NIR8 probe operates properly in the range of 2.01 × 10⁻⁷–1.29 × 10⁻⁴ M (UV–Vis), 9.81 × 10⁻⁵–1.52 × 10⁻⁴ M (fluorescence), and 2.92 × 10⁻⁵ M to 1.16 × 10⁻⁴ M (smartphone application) with a low limit of detection (LOD) (4.93 × 10⁻⁸ M, 9.86 ppb) (UV–Vis), (1.13 × 10⁻⁸ M, 2.26 ppb) (fluorescence) and fast (15 s) response time. NIR8 was successfully used to quantify Hg²⁺ in tap water, lake water and drinking water. In addition, Hg²⁺ was detected both qualitatively and quantitatively in MCF-7 and NIH/3T3 cells.