This work describes two sensing systems for the detection and quantification of Hg(II): (a) a highly tractable solid polymer membrane, and (b) a gelling system based on a low molecular weight gelator. The preparation of both sensory systems relies on a polymerisable acrylic monomer derived from a fluorene core containing a functional hydroxyimino group, which at the same time is an organogelator with Hg(II)-triggered gelating properties in organic solution. The polymerisation of this monomer with commercial comonomers gave a cross-linked membrane or film, which permitted the detection of Hg(II) using UV/Vis and fluorescence techniques due to the colour and fluorescence changes in response to the interaction of the film with Hg(II). At the same time, organic solutions of the monomer - or gelator - gave a gel upon interacting with Hg(II). Engineering of the gel formation conditions permitted the tuning of the visual detection threshold of the concentration of Hg(II), which ranged from 6 x 10(-3) to 1 x 10(-2) M in our study, while the membrane permitted the detection by UV/Vis and fluorescence spectroscopy of Hg(II) in organic and organic/aqueous media in the millimolar-micromolar range. Furthermore, the colour and fluorescence changes of the two systems were clearly visible, allowing for the naked-eye detection and broad quantification of milli to micromolar concentrations of Hg(II). (C) 2014 Elsevier Ltd. All rights reserved.