Acridine-Functionalized Fluorescent Nanofilm Toward High-Performance Detection and Visualization of Ethylenediamine Vapor

Achieving sensitive and visual detection of organic amines remains challengeable due to the lack of practical sensor devices and further effective commercialization of laboratory results. In this study, we first synthesized an aldehyde-functionalized acridine fluorophore and a hydrazide-modified calix[4]pyrrole derivative. Then, an acridine-functionalized fluorescent nanofilm (ACC) was successfully fabricated through interfacial condensation at the air-liquid interface. The ACC nanofilms feature the merits of excellent uniformity, tunable size and thickness, and good substrate adhesion, etc. Moreover, they demonstrate a ratiometric fluorescent response to ethylenediamine (EDA) vapor, characterized by a marked decrease at 510 nm in concurrence with a remarkable increase at 630 nm. This distinct spectral shift is clearly visible as a color change from green to yellow-orange. Disposable sensing strips based on the ACC nanofilm were developed for advancing practical application, enabling visual detection of the EDA vapor with a detection limit as low as 6.0 ppm. Integrated into a home-built sensing device, the ACC nanofilm performed as an outstanding EDA fluorescent sensor with favorable parameters of fast response (<3 s), low detection limit (1.2 ppm), and excellent reversibility over 80 cycles and can be practically applied for various scenarios of EDA detection related to contaminated items, container leaking, etc. Comparative experiments and theoretical calculations have elucidated that the NH site in acridine plays a critical role in enabling ratiometric sensing and regulating the strength of intramolecular charge transfer. This high-performance nanofilm not only presents an effective approach for real-time and on-site detection of EDA but also provides valuable insights for the future design of functionalized active adlayer materials.