Ultrasensitive quantification of Hg2+ in real samples using colorimetric, fluorimetric and smartphone-based triple-mode system integrated with a new indoline-fused chromenylium-cyanine chemodosimeter.

Mercury is one of the most toxic heavy metal, posing severe threats to environmental safety and human health due to its persistence, bioaccumulation, and detrimental neurological and systemic effects. Therefore, the development of fast, sensitive, selective, and on-site detection methods for Hg2+ remains an urgent priority. Herein, we present a phenylthiourea-derived indoline-fused chromenylium-cyanine chemodosimeter (INIR2), engineered as a "turn-on" near-infrared (NIR) fluorescent and colorimetric probe for Hg2+ recognition. Upon coordination with Hg2+, INIR2 undergoes a specific chemical transformation that results in a distinct color change and a remarkable fluorescence enhancement in the NIR region (λem = 766 nm) within 10 s. The probe exhibited ultralow detection limits (UV-Vis: 1.13 × 10-8 M (2.27 ng/mL); fluorescence: 1.83 × 10-8 M (3.67 ng/mL)) and outstanding selectivity among a wide range of competing metal ions. INIR2 also demonstrated robust performance across diverse matrices, including environmental waters (tap, drinking and lake) and food samples (corn and rice), achieving near-quantitative recoveries. Most importantly, the analysis of Hg2+ from micromolar to nanomolar levels (LOD: 2.10 × 10-8 M) was performed using a smartphone-based RGB application among molecular turn-on probes. This method has significant potential for cost-effective and real-time monitoring of Hg2+ in the field, even at ultra-trace levels. Cellular studies confirmed low cytotoxicity and selective fluorescence activation in Hg2+-treated cells, further highlighting its bioimaging capability. These findings demonstrate that INIR2 is a highly sensitive and versatile tool for instantaneous and on-site mercury detection, with promising applications in environmental monitoring, food safety and biomedical research.