Design and evaluation of sensory systems based on amphiphilic anthraquinones molecular receptors

A new paradigm is described that allows one to create different types of sensors: from highly sensitive ones to practical household devices. Our approach relies on modular molecular receptors incorporating an intensely-colored aminoanthraquinone signaling unit equipped with both hydrophilic and hydrophobic modules, the number and size of which being configured in accordance with the targeted analyte and the sought detection method. An important advantage is the compliance with some principles of green chemistry, avoiding the use of toxic organic solvents. The proper functionalization of the anthraquinone scaffold afforded water-soluble chromoinophores capable of quantifying selectively Hg2+ and/or Cu2+ in aqueous solutions down to the ppm level. The versatility of these ligands was exemplified by exploiting the self-assembling processes at the water–air interface of amphiphilic derivatives in order to produce metal-ion responsive films. The copper(II) and mercury(II) sensing properties of Langmuir monolayers floating on the water surface or transferred onto a quartz slice by the Langmuir–Blodgett technology have been investigated and are discussed. By adjusting the hydrophilic-lipophilic balance, ready-to-use dip tests could also be elaborated either by incorporating the colorimetric indicators in thick polymer films or by impregnating paper strips following a sol–gel process. These sensors possess the necessary sensitivity and selectivity for the direct determination of mercury and copper levels, as required for industrial-processes, waste disposal, environmental monitoring, clinical toxicology, or even for household applications.