Ultrasensitive and selective detection of MnO4− in aqueous solution with fluorescent microgels

The novel functional microgels, namely PNI-MSPC microgels, were fabricated via surfactant free emulsion polymerization (SFEP) by using N-isopropylacrylamide (NIPAm) as the monomer and a home-designed dichlorinated 1,1′-di[4-(vinyl)benzyl]-4,4′-pyridinium salt (MSPC2+.2Cl−) as the cross-linker. The PNI-MSPC microgels exhibited not only thermo-sensitivity but also redox actuatable hydrodynamic diameter and fluorescence properties. The PNI-MSPC microgels were successfully applied as the fluorescent sensor for ultrasensitive and selective detection of trace MnO4- anions in aqueous solutions. The presence of MnO4- anions led to the significant fluorescence quenching of the PNI-MSPC microgels with a fast response time of 5 min. The limit of detection (DL) for MnO4- anions can reach 25 nM with a linear concentration range of 0–50 μM. The co-existence of 16 other species of anions or 17 species of metal ions did not interfere with the detection of trace MnO4- anions in aqueous solutions. The potential applications of the PNI-MSPC microgels for sensing trace MnO4- anions in real world samples were also validated.