Surface charge tuning of functionalized silica cross-linked micellar nanoparticles encapsulating a donor–acceptor dye for Fe(III) sensing

In this study, a water-soluble Fe3+ ratiometric fluorescent sensor was designed and synthesized by encapsulating a donor–acceptor (D–A) dye 4-formacyl-triphenylamine (FTA) into silica cross-linked micellar nanoparticles (SCMNPs). The quenching of FTA-encapsulated SCMNPs (FTA-SCMNPs) on Fe3+ sensing was confirmed using the fluorescence titration method. FTA-encapsulated functionalized SCMNPs (FTA-NH2-SCMNPs and FTA-SO3H-SCMNPs) were synthesized to demonstrate the surface charge effect of nanoparticles on Fe3+ fluorescence sensing. The sensing ability of Fe3+ followed in this order: FTA-SO3H-SCMNPs > FTA-SCMNPs > FTA-NH2-SCMNPs, which indicates that particles with stronger negative charge have better sensing abilities. Moreover, linear correlation between the quenching intensity and lower concentration of Fe3+ was in accordance with the Stern–Volmer equation in FTA-SCMNPs and FTA-SO3H-SCMNPs. FTA-SO3H-SCMNPs showed good selectivity for Fe3+ detection. Because of the charge effect of functionalized SCMNPs on a dye-doped Fe3+ sensing system, these kinds of nanoparticles offered possibilities to construct sensing ability-enhanced fluorescence-quenching sensors by tuning the surface charge.