Optimizing Cu(II) luminescent nanosensors by molecular engineering of the indicator dye and the encapsulation process

Abstract

This paper describes the preparation of silica nanoparticles doped with a molecularly engineered luminescent Ru(II) complex for the selective determination of Cu(II) ions in aqueous media. Initially, three novel indicator dyes, namely [Ru(phen)2(L)]2+, where L is either hmpi (2-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)-4-methoxyphenol), haip (1-(4-hydroxy-3-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)phenyl)ethanone), or btym (N,N'-(2,2'-bipyridine-4,4'-diyl)bis(2-(thymin-1-yl)acetamide)), were synthesised, characterised and their response to metal ions was evaluated. The [Ru(phen)2(haip)]2+ complex demonstrated to be selective to Cu(II), so that it was embedded in 20-nm silica nanoparticles, synthesised by the Stöber method. The maximum sensitivity of the luminescent nanosensor was obtained when the indicator dye was incorporated 8h after the beginning of the 10-h silane condensation process, because interaction with the metal ions improves when the encapsulated luminophore molecules are closer to the nanoparticle outermost surface The nanosensor showed selective response to Cu(II) in the presence of Zn(II), Hg(II), Pb(II), Ni(II), Cd(II) and Fe(II) ions in 50mM phosphate buffer at pH 8.0, with a limit of detection of 0.30μmolL−1, RSD values lower than 3.0%, and a response time <30s. The nanosensor was applied to the determination of Cu(II) in mineral and tap waters spiked with 5.0 and 7.0μmolL−1 of the analyte, with recoveries from 88 to 110%.