Confinement-Assisted\nSpecific Fluorescence Detection\nof Fe<sup>3+</sup> in Aqueous Solution by Styrylpyrene-Based Microgels

In recent years, fluorescent sensors have played a compelling\nrole\nin the precise detection of metal ions. However, most fluorophores\nare hydrophobic and cannot be used to detect aqueous samples directly.\nResearchers have thus addressed this problem by combining fluorophores\nwith hydrophilic polymer carriers. Nevertheless, most studies have\nfocused only on the role of fluorophores in the recognition of metal\nions, ignoring the effect of polymers and their aggregation states\non the detection. In this work, microgels with pyrene-based fluorescent\ncross-linked structures were prepared using a post-cross-linking strategy\nand were found to specifically detect Fe<sup>3+</sup> directly in\naqueous solutions without interference from other metal ions (i.e.,\nAl<sup>3+</sup>, Ba<sup>2+</sup>, Cd<sup>2+</sup>, Co<sup>2+</sup>, Cr<sup>3+</sup>, Cu<sup>2+</sup>, Ni<sup>2+</sup>, Pb<sup>2+</sup>, Zn<sup>2+</sup>, Fe<sup>2+</sup>, Hg<sup>2+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, or Mg<sup>2+</sup>). The detection\nlimit is 2.3 μM, which is lower than the U.S. Environmental\nProtection Agency’s safety limit for drinking water. The fluorescence\nquenching of microgels by Fe<sup>3+</sup> was effective by both mechanisms\n(dynamic and static), mainly the static one. Nanoscale microgels allow\nFe<sup>3+</sup> to be confined around the pyrene of their fluorescent\ncross-linked structures, which induces nonradiative energy transfer\nand leads to fluorescence quenching of the microgels. Such a detection\nmethod utilizing the confinement effect of microgels to synergize\nfluorescence quenching provides an idea for the development of fluorescent\nsensors.