We developed -sensing chips by decorating the external surface of metal-clad optical waveguides with a monolayer of -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 ions. The fabricated samples were tested with optical waveguide fluorescence spectroscopy by putting them in contact with a 5-μM water solution of 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 as possible interfering analytes.