Ultrasensitive Fluorimetric Detection of Hg2+ Using a Thiourea-Based Chemosensor

Abstract

In this work we have successfully designed and synthesized a fluorescence "turn-on" chemosensor, TS-1. The structure of TS-1 was thoroughly investigated using ¹H NMR, FT-IR, and fluorescence spectroscopy was used for confirming its suitability for sensing applications. TS-1 exhibited a significant fluorescence enhancement upon binding with Hg²⁺ in a MeOH/H₂O (5:95, v/v) solvent system, demonstrating high selectivity when tested against various competing metal ions, including Pb²⁺, Ca²⁺, Na⁺, Zn²⁺, Al³⁺, Cu²⁺, Ni²⁺, Mg²⁺, Cd²⁺, Mn²⁺, Co²⁺, Cr³⁺, Ag⁺, and K⁺. The sensing mechanism of TS-1 was explored in detail using fluorescence spectroscopy and Job's plot analysis. The results indicated the formation of a strong complex between TS-1 and Hg²⁺ ions, leading to the disruption of a photoinduced electron transfer (PET) process resulting in fluorescence enhancement. TS-1 demonstrated exceptional sensitivity, with a detection limit as low as 0.0029 µg mL^-1, making it highly suitable for detecting trace levels of Hg²⁺ in aqueous media. The robust performance of TS-1 highlights its potential as an effective chemosensor for the detection of Hg²⁺. To validate the practical applicability of TS-1, recovery experiments were conducted using environmental and agricultural samples spiked with Hg²⁺ ions. The method achieved impressive recovery ranging from 93.00 ± 0.14% to 104.00 ± 0.54%, confirming its accuracy and reliability across diverse sample matrices.

Keywords: Chemosensor; Detection limit; FT-IR; Metal ions; PET; Thiourea.