A chemical sensor and a system and method for sensing a chemical species. The chemical sensor includes a plurality of nanofibers whose electrical impedance varies upon exposure to the chemical species, a substrate supporting and electrically isolating the fibers, a set of electrodes connected to the plurality of fibers at spatially separated points to permit the electrical impedance of the plurality of fibers to be measured, and a membrane encasing the fibers and having a thickness ranging from 50 μm to 5.0 mm. The system includes the chemical sensor, an impedance measuring device coupled to the electrodes and configured to determine an electrical impedance of the plurality of fibers, and an analyzer configured to identify the chemical species based on a change in the electrical impedance.