Monitoring of ammonia in the gas phase, a ubiquitous bulk chemical, is of paramount importance to ensure the safety of industrial workers. The present paper describes a solid-state optical ammonia sensor based on Forster resonance energy transfer (FRET) between narrowly dispersed blue-emitting carbon nanodots (CNDs) as FRET donor and fluorescein as FRET acceptor. The fluorophores were physically entrapped in a close to superhydrophobic sol-gel matrix, in turn deposited on a PVDF-HFP electrospun fiber membrane. The CNDs were synthesized via pyrolysis of ethylenediaminetetracetic acid (EDTA) in the presence of a hydrogen peroxide solution. X-ray photoelectron spectroscopy (XPS) confirmed a high surface coverage of hydrophilic groups, which is a result the addition of hydrogen peroxide in the reaction mixture. This translates into higher electrostatic interactions between ammonia and the fluorophores, in turn related to reduced FRET inter-distance between fluorescein and CNDs. If calibrated with respect to the fluorescein signal, the sensor shows a linear calibration with a remarkably low limit of detection, i.e. 110 ppb, and adequate reproducibility up to six N-2/NH3 cycles. (C) 2017 Elsevier B.V. All rights reserved.