A new near-infrared and multi-responsive thiazolyl ferrocene modified chromenylium-cyanine probe for ultrasensitive quantification of Hg²⁺ in real samples

Mercury poses a significant threat to both the environmental and human health due to its persistent, non-biodegradable nature and bioaccumulative behavior within the food chain. Therefore, the sensitive and real-time detection of mercury, even at trace levels, is of great importance. In this study, a new turn-on, near-infrared and multi-responsive thiazolyl ferrocene modified chromenylium-cyanine probe (NIR4) was designed and synthesized for ultrasensitive quantification of Hg²⁺ in the environmental samples and living cells. NIR4 was well characterized using several spectroscopic techniques. NIR4 was studied as a ratiometric turn-on probe for the highly selective and sensitive detection of Hg²⁺. New multichannel probe has a wide working range (0–5.00 × 10⁻⁵ for UV–Vis; 0 – to 8.32 × 10⁻⁵ M for fluorescence; 1.50 × 10⁻⁷ M – to 3.36 × 10⁻⁵ M for voltammetry), and a low limit of detection (LOD) (2.44 × 10⁻⁸ M for UV–Vis; 8.96 × 10⁻⁸ M for fluorescence and 6.02 × 10⁻⁷ M for voltammetry). The response time (<30 s) of the probe is notably faster than most probes documented in the literature. The probe exhibited a light yellow color, which turned green in the presence of Hg²⁺. The utilisation of a smartphone camera for the visual detection of Hg²⁺ was facilitated by the probe's colorimetric response feature. It has been demonstrated that NIR4 functions as a highly efficient probe, capable of conducting colorimetric, fluorometric, and voltammetric analyses of Hg²⁺ in real samples. Moreover, the molecular structure of the probe and its specific interaction with Hg²⁺ ions were supported by Density Functional Theory studies, and Hg²⁺ level was visualized in living (H1299 and Beas-2B) cells.