A methionine biomolecule-modified chromenylium-cyanine fluorescent probe for the analysis of Hg²⁺ in the environment and living cells

The objective of the study is, for the first time, to construct a new near infrared (NIR) fluorophore, spectrophotometric, colorimetric, ratiometric, and turn-on probe (CSME) based on chromenylium cyanine platform decorated with methionine biomolecule to provide an efficient solution for critical shortcoming to be encountered for analysis of hazardous Hg²⁺ in environment and living cell. The CSME structure and its interaction with Hg²⁺ ion were evaluated by NMR, FTIR, MS, UV–Vis and fluorescence methods as well as Density Functional Theory (DFT) calculations. The none fluorescence CSME having spirolactam ring only interacted with Hg²⁺ in aqueous solution including competing ions. This interaction caused the fluorescence CSME with opened spirolactam form which exhibited spectral and colorimetric changes in the NIR region. The probe based on UV–Vis and fluorescence techniques respond in 90 s, has wide linear ranges (for UV–Vis: 6.29 × 10⁻⁸ – 1.86 × 10⁻⁴ M; for fluorescence: 9.49 × 10⁻⁹ – 1.13 × 10⁻⁵ M), and has a lower Limit of Detection (LOD) value (for fluorescence: 4.93 × 10⁻⁹ M, 0.99 ng/mL) than the value predicted by the US Environmental Protection Agency (EPA) organization. Hg²⁺ analysis was performed in drinking and tap water with low Relative Standard Deviation (RSD) values and high recovery. Smartphone and living cell applications were successfully performed for colorimetric sensing Hg²⁺ in real samples and 3T3 cells, respectively.