Fluorescent chemosensory filter membranes composed of electrospun (ES) nanofibers and exhibiting a high sensitivity for pH and mercury ions (Hg2+) were prepared using poly(2-hydroxyethyl methacrylate-co-N-methylolacrylamide-co-rhodamine derivative) (poly(HEMA-co-NMA-co-RhBN2AM)) by employing a single-capillary spinneret. The HEMA and NMA moieties were designed to exhibit hydrophilic properties (absorption for Hg2+ in water) and chemical cross-linking (maintaining fiber structure in water), respectively. The fluorescence emission of RhBN2AM was highly selective for pH and Hg2+. Different compositions of poly(HEMA-co-NMA-co-RhBN2AM) were synthesized through free-radical polymerization, and their properties were explored. ES nanofibers prepared from copolymers with an 83.9:10.6:5.5 HEMA:NMA:RhBN2AM ratio (P3-1.0 ES nanofibers) exhibited an apparent color change from nonfluorescent to red fluorescent when detecting Hg2+, and high reversibility due to their capability of repetitive on-off switchable fluorescence emission upon the sequential addition of Hg2+ and ethylenediaminetetraacetic acid (EDTA). The P3-1.0 ES nanofibrous membranes had a higher surface-to volume ratio than those of corresponding thin films, which enhanced their performance, and exhibited a strong chelation capacity for Hg2+ of 94.82%. The prepared ES nanofibrous membranes with on/off switching capacity can be reused and applied as direct observation sensors, exhibiting the potential for application in water purification sensing filters. (C) 2017 Published by Elsevier Ltd.