Novel highly sensitive and reversible electrospun nanofibrous chemosensor-filters composed of poly(HEMA-co-MNA) and bpy-F-bpy with metal-ion-modulated multicolor fluorescence emission

Novel multifunctional fluorescent electrospun (ES) nanofibers exhibiting high sensitivity for various metal ions were prepared from binary blends of poly(2-hydroxyethyl methacrylate-co-N-methylolacrylamide) (poly(HEMA-co-NMA)) and 9,9-dihexylfluorene-2,7-bipyridine (bpy-F-bpy) by using a single-capillary spinneret. Different compositions of poly(HEMA-co-NMA) were synthesized through free-radical polymerization. The HEMA moieties were designed to exhibit hydrophilic properties, and the NMA content substantially affected the stability of the ES nanofibers in water. Experimental optical spectra and simulation results demonstrated that the fluorescent sensing probe bpy-polyfluorene-bpy could detect various metal ions. ES nanofibers prepared from copolymers with a 77:23 HEMA:NMA ratio blended with 5% bpy-F-bpy (P2-5) exhibited apparent color change from blue to green, color change from blue to blue-green and fluorescence quenching when detecting Zn²⁺, Hg²⁺ and Cu²⁺, respectively. The P2-5 ES nanofibers exhibited ultrasensitivity for Zn²⁺ (10^-7 -10^-3 m) because of the 70 nm red shift of the emission maximum, and high reversibility because of their on-off switchable fluorescence emission upon the sequential addition of Zn²⁺ and ethylenediaminetetraacetic acid cycled several times. These results and a microfluidics system study indicated that the nanofibers, which have a high surface-to-volume ratio, can be used as 'naked eye' sensors for sensing various metal ions and as efficient multifunctional chemosensor-filtering devices.