A fluorogenic sensory film, or dense membrane, capable of detecting Cr(VI), Fe(III), and Hg(II) in water was prepared. The film was prepared by a bulk radical polymerization of different comonomers, one of which contained a piperazinedione motif as sensory fluorophore. The film exhibited gel-like behavior and was highly tractable, even after being swollen in water. The sensing conditions were chosen to overcome interference from iron and mercury cations, giving rise to a material with a detection limit of 1 ppb for Cr(VI). (C) 2012 Elsevier B.V. All rights reserved.