Silica Nanoparticles for Fluorescence Sensing of ZnII: Exploring the Covalent Strategy

Silica nanoparticles (about 15 nm diameters), which contain a derivative of 6-methoxy-8-(p-toluensulfonamido)-quinoline (TSQ) as a ZnII fluorescent probe covalently linked to the silica network, were prepared and studied as ZnII fluorescent chemosensors. The systems selectively detect ZnII ions in water rich solutions with a submicromolar sensitivity: 0.13 mm concentrations of ZnII can be measured with the only interference of CuII and CdII ions. Compared with free TSQ, the nanoparticles based systems have the advantage that they can be employed in aqueous solutions without aggregation problems while at the same time, they maintain a similar ZnII affinity and sensing ability. Addition of a second, substrate insensitive, fluorophore to the particles leads to the realization of a ratiometric sensor.