Design and development of an onsite fluoride sensor: Time dependent-density functional theory approach and implementation

This study presents a novel colorimetric fluoride (F^-) sensor using the iron thiocyanate route, forming a hexafluoroferrate (FeF₆) complex. The sensing mechanism has been explored using Time-Dependent Density Functional Theory (TD-DFT) calculations, with computationally generated electronic spectra validated experimentally by UV–vis spectroscopy in the visible range at a wavelength (λ_max) of 455 nm. Computational studies provided more profound insights into molecular structure, electronic transitions, solvent effects, and the role of frontier molecular orbitals in the observed colorimetric changes. The optical sensor employs a photoresistor to quantify F^- via color intensity, achieving 0.46 mgL^-1 LOD and a 0.5–47.5 mgL^-1 detection range. Validation across 76 real-life samples yielded absolute % errors of 4.68–15.65 % and recoveries of 93.16–105.39 %. To the best of our knowledge, this is the first successful translation of FeSCN and FeF₆ computational studies into a portable fluoride sensor with the most cost-effective, rapid, and broad-range solution for onsite fluoride detection.