Bis-thiosemicarbazone functions as a selective chemosensor with the lowest LOD for Hg ions in water-rich medium: implications for on-site detection and logic gate experiments

Abstract

In this investigation, a mesitylene-anchored bis-thiosemicarbazone (TOMH), with the potential to chelate a metal ion via S,S donor atoms, was used as a chemosensor for the selective detection of mercury ions in an aqueous medium from mixtures with several metal ions (Ag, Al, Ba, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Th, and Zr). Electronic absorption spectroscopy revealed the composition of the identified species to be Hg(S,S-TOMH)·(NO₃)₂ (TOMHN). The spectroscopic (¹H NMR, ¹³C NMR, and FT-IR), theoretical (DFT and TD-DFT) and structural techniques confirmed the bonding of TOMH to Hg through S donor atoms (Hg–S: 2.484–2.490 Å and S–Hg–S bond angle: 160.1°), while the nitrates are non-bonded. The TOMH chemosensor has the lowest limit of detection (LOD: 10.97 nM) for Hg ions in a water-rich medium (90% H₂O : 10% DMSO) among thiosemicarbazones or closely related S donor chemosensors. It exhibits multiple applications, such as on-site detection of Hg using filter paper strips, formation of TOMH–Hg–EDTA-supported INHIBIT logic gate, and enhanced antimicrobial activity of TOMHN relative to TOMH or Hg(NO₃)₂ alone.