Sensing alkali and alkaline earth metal cations by conduction band quenching of dye photoluminescence

A new luminescence approach for sensing alkali and alkaline earth metal cations in fluid solution at room temperature is described. The approach is to utilize surface-adsorption/desorption-induced energetic shifts of a semiconductor conduction band to alter the electron transfer quenching efficiency of a photoluminescent dye. A proof-of-concept example is described based on TiO2 nanoparticles with a surface bound Ru(II) coordination compound as the dye, Ru(deeb)(bpy)(2)(PF6)(2) where deeb is 4,4'-(CO2CH2CH3)(2)-2,2'-bipyridine and bpy is 2,2'-bipyridine, sensing alkali and alkaline earth metal cations in acetonitrile solution. The Ru(II) compound is highly luminescent with long excited state lifetimes in the absence of the cations but is quenched in their presence. The quenching is found to be reversible. The data demonstrate that this approach yields intensity, lifetime, and wavelength-ratiometric calcium ion sensors that are sensitive to 5 X 10(-4) M concentrations.