Formamidinium iodide for instantaneous and fluorescent detection of Pb²⁺ in water

The visual and instantaneous detection of trace levels of toxic lead ions (Pb²⁺) in water is still challenging. In this study, a perovskite precursor-based fluorescent sensor for visual and instantaneous detection of toxic Pb²⁺ in aqueous media has been demonstrated. A solution of Formamidinium Iodide (CH₅IN₂) salt showed excellent fluorescence quenching ability upon the addition of Pb²⁺ due to the formation of perovskite. Interestingly, this sensor requires three seconds for visual and instantaneous detection of Pb²⁺ in the range of 1 μM to 1 mM, which is the fastest response compared to the literature reports to the best of our knowledge. Furthermore, this sensor showed a linear fluorescent response with various concentrations of Pb²⁺ in the range of 100 nM to 1 mM. The sensor also showed a low detection limit of 100 nM for Pb²⁺, which is lower than the safety limit of Pb²⁺ in drinking water. In addition, the sensor showed excellent selectivity against a variety of interfering heavy metal ions including Hg²⁺, Cr³⁺, Zn²⁺, Cd²⁺, Ag⁺, etc. The excellent performance of the sensor could be attributed to the high electrostatic potential energy of the formamidinium cation (FA⁺), which was calculated using Density Functional Theory (DFT), that makes FA⁺ highly interactive toward Pb²⁺. Furthermore, the sensor demonstrated excellent feasibility for the detection of Pb²⁺ in real water samples, which confirms its potential for testing Pb²⁺ in environmental samples.