Farewell to enzymes and organic solvents: an ionic liquid-based new paradigm for colorimetric sensing of Hg2+

Colorimetric detection of trace Hg 2+ relies primarily on enzymes -catalyzed 3,3’,5,5’-tetramethylbenzidine (TMB) reactions, with two inherent drawbacks: substrate solubilization dependence on organic solvents and enzymes-associated limitations. By virtue of unique structural tunability and ionic properties, ionic liquids (ILs) dual-substitute enzymes and organic solvents, breaking through traditional bottlenecks via electrostatic assistance. Specifically, ILs enhance TMB water solubility efficiently through π-π interaction/charge-assisted hydrogen bond (CAHB) synergy, thus obviating organic solvents; meanwhile, CAHB and electrostatic interactions accelerate TMB-Hg 2+ redox reactions, eliminating exogenous H 2 O 2 and enzymes s and cutting response equilibrium time by ~35   min. Experiments confirmed that vs. CAHB-free blank systems shows a 2.2-fold increase in absorbance. Moreover, the system exhibits robust anti-interference, maintaining high sensitivity and stability across the pH range of 4.0–6.0. The paper-based ILs sensor allows naked-eye, on-site detection of trace Hg 2+ efficiently.