We developed Hg2+-sensing chips by decorating the external surface of metal-clad optical waveguides with a monolayer of Hg2+-sensitive fluorescent molecular probes. The emission properties of the original water-soluble form of the molecule were previously found to be selectively quenched in the presence of Hg2+ ions. The fabricated samples were tested with optical waveguide fluorescence spectroscopy by putting them in contact with a 5-M water solution of Hg2+ ions and recording the emission spectra versus incubation time. The estimate of the limit of detection was 150 nM. A preliminary evaluation of the selectivity of the structure was also performed by using Cd2+ as possible interfering analytes. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)