The fluorescence quenching of molecules by analytes of interest, is a widely employed phenomenon in fluorescence sensing technology. Forster type dipole-dipole energy transfer from dye molecules to transition metal ions, provides a method of monitoring the concentration of these ions with some degree of selectivity. Each metal ion has a different absorption spectrum, hence, in principle it is possible to choose different fluorophores for each metal ion. In the present work, quenching studies of the carbocyanine dye DTDCI by transition metal ions in a viscous solvent and a Nafion polymer matrices are reported. The potential for fabricating near-infrared energy transfer sensors is assessed, particularly with regard to detecting copper ions in solution.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.