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

Abstract

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.